A beautiful box with a simple design and clean lines. It is black and not gray as it appears in most photos. It fits in any space and would be even better if there was an option for a metal side panel (made of glass) for a more "serious" appearance without lights and other "Christmas" effects. But nowadays it is difficult to find such boxes without transparent sides and LEDs, because manufacturers (including CoolerMaster) consider us all gamers. As for the NR600 (and its smaller brother, the NR400), the front perforated metal acts as a dust filter, allowing the light from the lights that will decorate it to diffuse. This way, you have very good airflow, especially if you add a tower cooler to the processor. Keep in mind that the provided fans will go to recycling as soon as you open the package. Nothing special, and I don't know why CoolerMaster still uses 3-pin fans instead of PWM fans. Also, I don't know why they removed the motherboard's Beeper or Buzzer that used to come with their cases. There are some minor imperfections in the paint (fortunately only on the inside). The accompanying accessories (screws, etc.) are all loose in a bag. In general, in the overall effort to reduce costs (1-2 euros if you calculate it), several cuts have been made that fortunately are not a reason not to choose it for your new system (or to transfer an older one to a new case for better appearance and airflow).
Finally, the NR600 and NR400 are sibling cases to the Silencio S600 and S400 respectively. The differences are that the Silencio cases are quieter, soundproofed, with 2 Silencio FP120 PWM fans, but not the same airflow.

There was a difficulty with the insertion of the power supply and the cable management (I have a full modular power supply). It is a bit tight on the top of the motherboard, making it difficult to insert cables, especially if you have a top fan. However, both cases can be resolved with a little perseverance.

CoolerMaster Masterbox NR600 (No ODD)
Purchased 1-1.5 years ago for 72 euros (including shipping and handling charges).

I chose it for its good and potentially flawless (+1 fan) airflow in relation to its cost, based on the reviews I saw (For example, the airflow values recorded by Steve Burke, also known as Gamers Nexus, with this particular model and an additional fan-case rank it quite high on the database list he maintains, compared to more expensive or newer models).

Build Quality:
Good. Steel, tempered glass, and plastic-framed steel mesh case.
Sturdy and relatively heavy. In my case, it doesn't creak, the tempered glass fits perfectly on the case, and overall, I didn't find any other minor flaws.

Cable Management:
Relatively good, but there are definitely much better options.
Nevertheless, even as a relatively novice user, I didn't encounter any serious issues with cable management using a full wired power supply and 2 SSDs.

Pros:
Very good airflow.
With the addition of a case fan (120 mm), the airflow becomes more effective compared to more expensive cases.

Cons:
The PSU cage entrance could be slightly larger.
Dust filtering is mediocre.

[UPDATED]
In addition to the 2 fans that came with the case, I also installed an additional directional fan (Noctua NF-S12A chromax.black.swap) in the top front slot as recommended by Cooler Master. The result was a 2°C drop in GPU temperature, and an even more noticeable drop in CPU temperature, as now (in addition to the middle front stock fan that generally introduces air) there are 2 aligned fans (one front top and one rear) that create a stronger and more compact airflow, mainly passing through the RAM and the stock CPU cooler. Any excess air (which cannot be removed by the rear stock fan of the NR600) is mostly expelled from the rear exhaust at the top of the case.

A reliable product for its price.

Mesh in the front + tempered glass = recipe for success.
The case has a very good design for cooling and plenty of space for cable management at the back. It has dust filters and the mesh in the front is excellent for dust filtering. The feet are soft for shock absorption and high enough to provide sufficient airflow to the power supply.

Unfortunately, it also has some negative elements.
The placement of the power supply is quite difficult, and it gets worse as the power supply gets bigger. If you have a modular power supply, connect the cables before installation.
The drive cage for the hidden 3.5" HDD cannot be removed. The locking system does not absorb shocks, so vibrations are transferred throughout the entire case, resulting in excessive noise.
It offers a set of plastic shock absorption screws for fans, even though the case supports up to 6 120mm fans.
The 2.5" disk slots in the front require either power cables with sufficient length or extenders. Otherwise, forget about them.
The case claims to support 2 140mm fans in the front, but the holes (for the fan, not the screws!) are not big enough. Unless you're willing to do some modifications, it's better to prefer 120mm fans.

Despite the negatives (flaws that can easily be overlooked or bypassed), at around €80 (including shipping), there is no better solution than this case.

The case is beautiful but if you have multiple hard drives, you will encounter problems with cable management and configuration because it does not have traditional disk bays and the disks are suspended here and there.

Also, as a construction, it is not very compact and it creaks either when the CPU fan speeds up or when the HDD is working.

In the end, besides beauty, I don't know what this case offers compared to a cheaper one.