I have an Apple Thunderbolt Display and a generic 4k. The Apple display powers on instantly, the speakers are fantastic, it functions as a dock, and I can control brightness from the keyboard. The generic 4k display has none of those benefits, oh and I can't seem to get accurate colors.

I was prepared to buy a new Apple display today knowing that it would be quality in all those aspects. Instead it'll be trial and error to discover a good monitor that works as well as Apple's aging thunderbolt display.