I got this monitor in yesterday and got my buddy to bring his 34GK950F down for some comparison. Here are some thoughts for whoever is interested:
A photo of it set up -
https://postimg.cc/SYSyTgVv
Build: the screen without the stand is slightly over 7kg due to the built-in speakers and power supply, so double check your monitor arm specs if you're planning on mounting it that way
. Top and side bezels are flush with the screen and very thin - around 5mm. The chin is thicker, like on LG's monitors. The plastic is flush with the display and there is no play in the casing when applying pressure, which is always nice. The OSD is controlled via 5 separate buttons instead of a joystick, which would have been better. The power button is slightly apart from the rest, at least, which helps in getting used to the layout.
Flat screen: I come from a 29" flat monitor, so going up to this 34" hasn't really been a problem at all. It's only 2.3" wider on each side than my old display, or compared to a 16:9 flat 32" - 1.7" wider on each side.
Matte Coating: It's thicker than the one LG use. If you look at a white page from a foot away you can spot the "crystallised" pattern. That being said, I spend a lot of time working in Excel on my PC, which is pretty much a worst case scenario for this - black lines and text on a white background, and it doesn't bother me at all. I sit about 32" away from the monitor.
Colours: I don't have a colorimeter but they looked nice and vibrant compared to my old 29" LG IPS. Colours on the 34GK950F were more oversaturated and vivid by comparison due to its wider colour gamut. The monitor supports 10bit processing (8bit + FRC). The viewing angles aren't as good as on a curved 34". There is some slight discolouration right near the edge of the side bezels. E.g. discord active channel tab graphic or fullscreen scrollbar
Brightness: Definitely bright enough. I have it set at 25/100 throughout the day. My metric is being able to open a full white screen without feeling discomfort.
IPS glow: 4 small yellow patches of glow near each of the four corners. A big orange patch near the bottom left corner. The latter causes some discolouration even when using the monitor in a well lit room, effectively making the left 20% of the display look warmer than the rest. Overall, I'd call this above average - worse than LG's old panels (X34P, AW3418), slightly worse than their newer ones (34GK950F). Don't buy this if you are planning to mainly game in a dark room. Of course there is a lot of variance here, so take my sample point with a grain of salt.
Response Time: there are 5 levels of overdrive in the OSD, ranging from -2 to +2. "+2" shows some strong haloing straight away at 144Hz, so probably not usable for most people. "+1" has minor inverse ghosting, but barely noticeable. Played an hour or two at that setting at both 60Hz and 144Hz and am satisfied with the performance - there is no dark level smearing like on VA panels. The ghosting is a bit worse than the 34GK950F in the UFO test. Overall, I'd say this is practically a 120Hz monitor. Bumping the refresh down from 144 to 120 shows a visible reduction in ghosting trails in both UFO test and general use like moving windows around & scrolling in discord or a browser. I didn't notice any problems with input lag. I also didn't test the MPRT mode because I rather have adaptive sync.
Adaptive Sync: I haven't had the time to test with an Nvidia GPU yet. On my Vega 64 I tested Freesync both at 144Hz, 30Hz and 45-50Hz (around the LFC activation range). No tearing, flickering, stuttering or any other problems of note. The "Freesync Premium" standard seems to be implemented well here.
Overall: for the price this is a cracking good display in my opinion. The biggest downside for me is the glow level, but it's not a deal breaker. I would also have liked to see a software app to control the OSD, hopefully iiyama can develop one eventually. I'll probably get the 34GN850 from OCUK to check it out, if they get stock this month, but I doubt it will be sufficiently better to justify at ~£600 premium.
