I have it here for about 2 weeks, former owner of Razer Naga and I am a Video Editor.
I got it for my Macbook since you can't do work without a mouse.
You get used to its weight and design in the first 2-3 days, but from then on, the side scroll wheel and the new technology of the main scroll wheel will give you a hard time getting used to.
Of course, through the Logitech App, you can adjust EVERYTHING... so once you get it, it is a MUST to download the App and experiment with how the mouse suits you. Once you find the right settings for you, the mouse works wonders and you won't want to go to another one!
The build quality is sturdy with enough weight for a mouse, I don't recommend it for people with small hands or left-handed people. Its battery is incredible, I read that it lasts about 3 months, which might be true since I haven't charged it for 2 weeks now. Finally, it experiences some occasional glitches as a device, especially with the scroll wheel, but they can be solved with a quick Turn Off and Turn On from the Mouse, which takes 2 seconds!

The truth is that I expected it to be slightly better than it is rumored. I ordered the regular version and not the one for mac. It came with the classic problem that many encountered. The scroll wheel was damaged. The patent that Logitech made with the magnet couldn't handle all the scrolling I did and lost about a third of it, something that many YouTubers mentioned and I knew beforehand, but I thought, could I be so unlucky to get a defective one? And yet it happened. Luckily, I did the right thing and bought it from a well-known chain store, and they replaced it on the spot. At this point, I want to emphasize that the technical check showed that there was no problem, which I cannot accept, but they told me that I have the right to get a refund or buy something else. Therefore, I didn't pay much attention to it, and as a replacement, I decided to get the same one in the for mac version since I use it on a MacBook Pro M1. This time it didn't have any defects, it works fine, but the scroll wheel still doesn't impress me... I still notice some steps being lost when I scroll in succession with a constant pace. For this reason alone, it loses a star because I have no complaints about everything else. The construction is of good quality, the battery lasts about a month, nice design (I didn't notice what others say, that it tires their hand and it's not ergonomic), and the side scroll wheel is very pleasant. Overall, quite satisfied! I would just advise you to buy it from a well-known and large store because the chances of getting a defective one are quite high.

EDIT 2+ years later:

Nothing has changed in my opinion about the mouse... It's pretty good as I mentioned above, but not perfect. The only (daily) problem is the scroll wheel. You will never scroll with absolute precision. At the office, whoever used my computer would say "why is the mouse like this", "what's wrong with the scroll wheel", "how do you manage with this", "this is supposed to be the best productivity mouse on the market?" and such. I partly agree since it is indeed one of the top 3 mice for productivity (possibly the best, especially with the 3S version), and when you pay for the best, you want to have it. Many YouTubers present it as the "ultimate mouse," but if you dig deeper, you will see that there are many who show it objectively. However, for 2 years of use, I can say that otherwise, it is as it should be. Excellent grip design, works flawlessly on all surfaces (desk, table, sofa, glass table, thigh, everywhere). Apart from what I mentioned, it didn't present any other problems along the way, and it seems like it will last for many more years, unless they release a version 4 that is different from the 3 and 3S. We'll see. At this price, however, it's better to go for the 3S version due to the silent switches.

I got it for my job, so I use it for at least 8 hours every day for about 2 months.

Pros: Ergonomic and comfortable. The extra buttons, especially the Forward/Backward button, are very helpful and convenient. It has great precision in the movements you make as long as you have the right mousepad or surface (read below). Finally, the battery life is very good, you completely forget to charge it. I think I charge it once a month and it charges very quickly. It works well on many surfaces (plastic, wood, etc.) without any issues.

Cons: It disconnects, which is very annoying. About 1-3 times a day, while working on my PC for at least 8 hours (MacBook Pro with Big Sur). I have tried various solutions but none of them worked. Luckily, it has a button underneath that reconnects it, so reconnection takes a few seconds. You just don't expect this from such an expensive mouse. Lastly, at least on my soft cloth mousepad, it was not comfortable to move and it gave me more trouble than my previous cheap and lightweight mouse. However, it works fine on a wooden table or a glossy mousepad.

Overall, I don't know if I would recommend it for its price due to the above issues, but the scale leans towards positive due to its ergonomics.

-----

EDIT: A few months ago, after an update through the Logitech App, the disconnects have completely stopped. It is now flawless, so it goes from 4 to 5 stars.

When you buy a mouse for around 100 euros, you expect one very simple thing. Excellent connectivity with the computer. Especially in the case where the mouse is intended for Mac (and therefore for a few models), there should be a direct connection of the mouse after the first time.

Although I saw excellent comments in reviews on YouTube and Skroutz, from my personal experience, the mouse frequently disconnects (not at random times, but after restarting the computer), the Logitech application is not particularly informative, and it asks for unnecessary access to the computer.

Therefore, I do not recommend the mouse to anyone.

Ignoring the issue of connectivity, it is a very good mouse, it feels quite comfortable in the hand (it would be perfect if it didn't force the two outer fingers to touch each other), the buttons are also quite good, and the scroll wheel is great (especially if you write code and need to scroll through multiple lines quickly).

As for battery life and durability in case of drops, I have no opinion because I haven't had the product for a long enough time.

P.S. Obviously, I am being harsh in my criticism due to the price and advertising of the mouse. Compared to a simple mouse, your hand will feel superior.

I was using the magic mouse 2, which due to its size was ideal for me to always have it with me in my laptop bag. Due to the quarantine and restrictions on movement and working from home, I got the MX Master 3 for Mac.
Advantages: It is clearly more comfortable and ergonomic in the hand. Scrolling with the large and high-quality wheel is faster and more convenient compared to the touch style of the magic mouse 2. As soon as you turn on the Bluetooth on the MX Master 3, it quickly connects to the Macbook without interruptions or other annoying issues, and I consider it to be much better and more immediate than the magic mouse 2 (no matter how exaggerated it may sound). Many customizable buttons to adjust it to each person's needs (through Logitech software that works perfectly and gives you many customization options for the buttons, scrolling speed, etc.). Also, it is very positive that it charges from a port located in front and in a position that allows you to comfortably charge it while working - something that cannot be done with the magic mouse 2 as its charging port is on the bottom. Battery life is quite good. I use it daily for about 3 weeks and it has consumed about 1/3 of the battery. So, I estimate that with normal use, it lasts for more than 2 months (so you charge it 5-6 times a year). In terms of speed and responsiveness, there is no discussion - it is flawless. Even the 2-3 times I have used it for gaming, it performs quite well for a Bluetooth mouse.
Disadvantages: Although it is premium and generally has very good build quality, it gives the feeling that its materials are slightly inferior compared to the magic mouse 2. The buttons are a bit noisy, which of course is subjective as to how much they bother each person. Personally, I got used to them and they don't bother me much. One last thing that I didn't like is that when you quickly place your hand on it, you can accidentally move the side wheel a bit and (depending on the setting and sensitivity) it can change, for example, the zoom in a document or move a table you are working on.
Overall conclusion, it is an ergonomic, good quality, and reliable professional mouse, but I recommend it more for someone who works at a fixed desk and is not particularly concerned about portability (due to its size).