There are countless reviews for this specific model of Sennheiser. Most reviews are positive and very few are negative. I decided to purchase them and chose them over the 6XX series, based on these reviews and the price difference. I enjoy the flat sound, as my ears have been trained from a young age for this type of sound. In combination with the Fiio E10K Olympus 2, I have a super clean sound, flat but with a bit of bass color if I want. I mainly listen to classical and jazz, but also 70's classic rock, R&B, and 80's indies. For the money I paid, less than 150€, I am completely satisfied with the result.

The build quality is as expected from the company. Good quality plastic, lightweight, comfortable, they disappear relatively quickly and you can listen to music for hours without fatigue. It is a newer model and differs from the original in the cable and the connector, which is 3.5mm with a screw-on 6.35mm adapter.

I highly recommend them.

--- update 11.04.2023 ---
I listen to them all day. Even from YouTube, they bring out every last detail that exists.
I read the reviews, was convinced, bought them, and they are incredibly better than I expected.
I emphasize that they are flat, they don't have any "color," they don't have a "sweet" sound, and that's why in combination with iZotope's Ozone or the Fiio E10K, you can bring them to where you want, if you desire more bass, color, sweetness, you can "tighten" or "spread" them, something you can't do with headphones that already have their own "character." For Jazz, Classical, Ambient, Progressive, you will enjoy everything you liked from the past and be impressed by the clarity, sound stage, and the fact that they "disappear" due to their low weight and comfort.

For music and gaming, they do their job very well. Keep in mind that you will need a microphone. I tried the V Moda Pro, but it doesn't fit because it requires a 2.5mm adapter, not a 3.5mm one. In terms of sound, they focus on clean vocals with neutral mids and slightly crisp highs. So, for FPS games like COD/Warzone 2.0, they do a great job without hurting your ears. However, don't expect drastic differences. You can achieve the same results with the Cloud 2 for Warzone 2.0 for under 80 euros, with a bit more emphasis on close-range footsteps inside buildings, but you may experience ear fatigue. These headphones are open-back with reference sound, which emphasizes music listening without hurting your ears and with excellent stereo imaging (you can precisely determine the direction of the sound). That's why their price is higher. Additionally, they are easily driven, so you won't need a DAC if you have a relatively new motherboard. EDIT: (I got an ifi Zen DAC V2 and connected them, and it improved even more in terms of gain and clarity since this particular DAC matches very well as it doesn't color the sound).

As the owner of other headphones, including the 560s for over a month, I have the following to say:

SOUND: quite neutral, they don't have a crazy character, suitable for all genres of music, they don't have the WOW factor, I recommend them if you produce music rather than just listen as a HIFI audiophile... however, I was impressed by the clarity and separation of vocals and instruments in the midrange... you can hear the difference between a trombone and a clarinet, etc... also, the fact that they reach up to 38kHz, even though you can't directly hear it (a baby can hear 18-20,154Hz and it worsens over time), it manages to produce a more defined sound in the 14k-20k range and has better clarity compared to 50mm drivers - magnets... these have the enhanced 38mm technology by Sennheiser's EAR, which has a triangular foam inside that helps widen the sound stage - the "air of the stage".

FIT: They are relatively snug on the head, but not to the point of feeling like jelly... you can comfortably wear them for 3 hours since they are lightweight and of the open type, allowing your ears to breathe.

I also liked the fact that they have a 3-meter cable... subjectively, it may not be the most practical if you don't intend to use them in a studio with instruments that are far away, etc...

Lastly, the 120-ohm impedance is on the "heavier and more demanding" side, as many sound cards sacrifice signal purity to capture the mV, so either you don't have enough volume, or you have volume but the sound loses SPL due to reducing the dynamic range significantly, making them more "insensitive" at different volume levels... for example, if you have a Scarlett Solo Gen3, it will sound low, if you have a U-Phoria UMC22, you will have noise due to poor amps and excessively dirty signals... they will shine on a Motu M2 or an Audient iD4 MKII...

From me, for anyone serious about music production and doesn't already have a set, I would recommend either these headphones or the 80-ohm BeyerDynamic DT 770 Pro... otherwise, for use with mobile devices and small gadgets, the 32-ohm version.

P.S.: I also have a video of my unboxing and opinion here:
https://www.youtube.com/watch?v=uLxyILLQ46M

It took some time for me to have a complete picture. First of all, I have to clarify that for those who are Harman lovers, these headphones are easily 5 stars. In terms of construction, they are exactly the same as the HD 599 and basically the entire 5 series. They do not have an extra cable included, nor do they have a balanced cable. For those interested, they can be found online as extras. They have the classic large cable that Sennheiser provides, which can be a bit cumbersome. There are a few creaks in the headband, but I know from experience that they go away with time and wear. I also noticed that they were very tight on the head compared to the 5 series, but they will definitely loosen up, unlike the HD 25 which never loosen up no matter what you do. The earpads are the classic velour ones from the 5 series, with the classic foam inside. In my opinion, they are very good pads, although I personally prefer the earpads of the HD 6 series. They have a greater depth compared to the HD6, basically the same as the 5 series. They even have the same padding inside. They have a large soundstage and are very comfortable and lightweight. The cable, for those who don't know, is on one side and passes through the headband, which makes them more sensitive compared to headphones that have cables on the outside and on both sides. It is also easier for those who are handy to make their own cables. Now let's talk about the sound... It is definitely something completely different from what Sennheiser has accustomed us to. It has absolutely no resemblance to the HD 5 series. It lacks that warmth, that deep bass, that dark character... These headphones are flat, and when I say flat, I mean flat... They may seem bright to some who are used to the sound of Sennheiser, but that goes away with time and as your ear adjusts. They are definitely not as treble happy as Beyer, so don't be scared. They are just a click above what we know. When I put them on, they reminded me of the Sundara, although they didn't follow in terms of technical performance, meaning they didn't have the same speed or resolution... Nevertheless, they were quite close, and I'm sure those who want to spend half the money will enjoy them. Overall, I believe they are the best solution for 200 euros... You might ask why I gave them 4 stars instead of 5? The reason is simple and has to do with the musicality, the volume, the fullness in the sound that is missing here compared to the HD 600, 650, 660s. Even though the 560s are more correct in practice, you miss that warmth, that body in the sound, the vocals that are inside your head, that timbre... The 560s, compared to the 6 series, are colder and more analytical... However, the musicality, the smoothness of the 650 and 660, is on another level, much superior, and at the same time, they don't lose in terms of resolution... It's there, it's just not as upfront as the HD 560s, which have a similar air to the Sundara. If you don't listen side by side with headphones that are twice or three times the price of the 560s, then you can't see these small differences... And to be honest, if I had a limit and could only have one pair of headphones in the 180-200 euro range, I would still choose the HD 560s over the HD58X... But if I had the choice between the HD 560s and the HD 6XX, 650, 660s regardless of price... I would go for the latter for the reasons I mentioned earlier... But that's just my personal preference... If you are Harman lovers and strictly need them for work, then definitely go for the 560s.
Those of you who have the HD 6 series, I would also recommend getting them as an alternative headphone. You will also like to have something different, just like me. If you have headphones like Sundara + 400i 2020, my opinion is to put Harman EQ on the Hifiman and keep them... The only reason for the 560S would be that they are much more comfortable, lightweight, and easy to drive, even from a mobile phone.

Ps. For those who are too lazy to read... 560s are excellent flat harman target headphones that lose in musicality and technical background compared to the 6 series.

Okay, what can one say about this new implementation by Sennheiser. After the Fostex T50RP Mk3 and the Beyerdynamic DT880 Premium Edition 600Ω, which I considered (until now) the benchmark in this category, I never expected that another headphone would come out that could not only be compared to them, but also surpass them in every aspect (sound, comfort, ease of use, weight), and I'm talking about headphones up to €200. Let me be more clear, after I talk a bit about their build quality, which is not something extraordinary. You can tell at first glance where the cost-cutting measures were made so as not to compromise the sound quality. The construction materials are similar to the other headphones in the 5XX series, with a lot of plastic and a simple and minimalist design.

And I immediately move on to the sound. Their bass is tight and fast for a dynamic open-back headphone and can only be compared in speed to the planar headphones by Fostex. The mids are crystal clear and tonally accurate, and you feel like the vocals are coming right in front of and around you. Combined with the slightly boosted highs (a slight peak around 4KHz-6KHz and 8KHz), they provide incredible clarity and detail with an exceptional stereo image that even triple the price dynamic headphones would envy. Their soundstage is also exemplary for this category, being open-back headphones, and of course, with the appropriate range that distinguishes Sennheiser, especially in its more expensive models. I won't bore you with more details about the sound, analyzing how close or far they are from the Harman curve, because what ultimately matters is how each person's ear perceives the frequency spectrum. For the record, though, they are some of the flattest signature headphones on the market.

In terms of comfort, the company has done a great job here as well. The headband is made of soft foam material that doesn't strain the top of the head, and the clamping force is just right, giving the feeling of a lightweight and comfortable headphone. Of course, I don't have a huge head, so I never encountered such problems with circumaural headphones. The pads are made of soft velour and also contribute to the maximum comfort level. During the summer months, prolonged use of them might be uncomfortable, but personally, it's something I can compromise on.

Driving them is easy and can even be done from a smartphone, although having an amplifier would still benefit them, especially if it's a tube amplifier.

The only negative thing I can point out is the excessively long cable that they come with, without any other alternative included in the package. However, you can easily find a solution for this since they can accept cables from other models by the same company, as well as cables from the "M" series headphones by Audio Technica (M40x, M50x, etc.).

In conclusion, I believe that for this price, it's hard to find other headphones that are as well-rounded and check so many categories. And of course, when their price drops to around €150-160 in a short while, they will be the ideal purchase.
All of the above, of course, reflect my own opinion and image that I have for these specific headphones, based on my experience so far with dozens of other headphones that have passed through my ears. And because I don't want to deceive anyone, especially since times are financially difficult, the only thing I can tell you with certainty is that if you are in the market for new headphones and have the opportunity to listen to them somewhere, do it.