I bought this monitor (which is one of the most expensive in its category) to combine it with the following:
1. PS5
2. Laptop (Macbook pro)
3. ipad (the rare occasions I need to do something quickly and the laptop is at work for example)
4. steam deck

Starting with the advantages:
1. It has an amazing panel with local dimming and very nice HDR. The blacks are also very nice (and really black, not dark gray)
2. I really like its design, as well as the stand. It has an RGB LED bar at the back that constantly gets compliments from anyone who sees it in my home office.
3. It has a very small bezel around the panel
4. It plays nicely with the PlayStation 5 (has HDR profiles, optimized things for framerates, etc.)
5. In terms of specs and connectivity, it's very good (e.g. HDMI 2.1 that provides 4K 144Hz over HDMI, USB hub with device charging, etc.)

Moving on to the disadvantages, which unfortunately are many and EASY TO FIX IF SONY DEALS WITH THEM!!!

1. A selling point is the auto KVM switch. If you have multiple devices, it automatically switches to the right input. However, this doesn't work as expected. Most of the time it takes 30+ seconds and then may blink 1-2 times. So when you boot up the PS5, you have to wait, or when you turn it off, it takes a while to switch back to the laptop. This gets worse with the Thunderbolt 4 dock I have with a USB-C connection...
2. The monitor's firmware can only be installed through Windows!!! If you don't have Windows, it's IMPOSSIBLE to do. I don't have it and I have to use a borrowed laptop. It doesn't work even from a Windows VM. Their software is called Inzone Hub and it's kind of garbage, but you don't need to use it more than once a year.
3. Its speakers are terrible (personally I don't care but I mention it).

A few words if you're stuck with the firmware update, which must be done (you see a huge difference every time), so you don't struggle like I did until I figured it out:

1. You need to connect the monitor via USB to the Windows machine running the Inzone Hub.
2. Disable any other monitor (if you have a laptop, disable its screen so you only have the Inzone).
3. The USB-C is on KVM switch 1 and the USB-B is on KVM switch 2. So if, for example, you have the monitor on HDMI 2 and USB-C, select KVM switch and HDMI 2. Disable the other KVM switch.
4. Reboot the laptop and unplug the monitor for a minute.
5. Update the firmware from the Inzone Hub.

You can also see here: https://www.sony.com/electronics/support/monitors-inzone-m9-series/sdm-u27m90/software/00284042

These are not serious things I believe but okay. I spent an hour each time until I noted them somewhere. In the M010 update I'm on, my biggest problem, which is the delay when it automatically switches inputs, seems to have improved significantly.

So in simple terms:
- Is it a good monitor? Yes, it's excellent. It has really crazy specs and not just on paper. Sony can do wonders with the image.
- Is it worth €1200? No, get the equivalent LG, Asus, Gigabyte, or Samsung for €700-900. Unless you care about the appearance and PS5 HDR profiles, which I think is worth it. (edit: especially now that it's around €1000, I think it's worth more.)
- Would I buy it again? With great pain, because there are many things that are annoying, maybe yes.