I think there are 3(4) caveats when using a 4K instead(not counting the fact it's not curved, cause expensive).
?0th? - Durability - some articles have made me doubt that 4K Tv's can take the abuse of being used for as much hours as a monitor.
1st - Picture quality - readability of text, lack of blurriness and sharpness(either one is bad), not tiring one's eyes.
2nd - Ports, most are HDMI 2, but in fact most VGA's only have DP1.2(which has enough bandwidth) and HDMI1.4(doesn't).
3rd - Window positions, with multiple monitors - we rarely place a window on more than one monitor. Hence it's like we are tilling, cause we can maximize too.(and I doubt many ppl keep more than 2 open windows per monitor) But in fact most of us are using a stacking window manager - ie. All Windows window managers(no idea how they are called), kwin, etc.
And they suck for one monitor.
Hence I think - a 4K requires using a tilling manager as to be able to maintain multiple non-overlapping windows -
https://en.wikipedia.org/wiki/Tiling_window_manager