I didn't have too much time for testing today, and a lot of it was needed to get it to run at more than 24 Hz. The 15' DP 1.2 cable
(from UGREEN, "4K Resolution") I had bought for this did not work well. Even at 1920x1080 I could only select 24 Hz (or 23 Hz, depending on the dialog - Windows vs. NVIDIA). After enabling overclocking, I was able to select all resolutions, but any above 24 Hz (even 60 Hz) would crash the graphics card. Luckily it auto recovers after 30s or so, and using my TV as a second monitor I was able to play around with the settings.
With the included cable, however, it works well, even at 165 Hz! So if anyone has a 15' DP cable that works well with high resolutions and refresh rates, let me know, I need one.
So far I'm happy with the display! It looks great, the picture quality is good (definitely better than the 19" Samtron 94B I was using before), the size is great, text looks great because of the high PPI.
I tried Rainbox Six Siege for a bit and G-Sync appears to work as well. Getting around 100 fps at 1440p and Ultra settings (and using the HD texture pack), but it varies. Looked smooth for the most part anyway, except occasionally there's a complete 1s stutter. Not sure yet what that is about, I don't think that happened with my old monitor. Also, the intro videos stutter every 1s.
Played at 1080p for a bit, it's definitely playable, but noticeably blurry. Not ugly, but not great either. If you get a high end card in a month or so, you can put up with it until then, but I wouldn't be happy with it as a long-term solution.
I tried the testufo.com pixel inversion test and see a flash every second regardless of the other settings. That is not what I expected to see as a result of pixel inversion issues, sounds like something else.
As far as the coating is concerned, it is definitely matte, but I have no idea whether it's light or not. Maybe this picture helps (monitor off, just a reflection of my windows), if not, let me know what I should try: