Any external Monitor, which matches iMacs quality on the market?

[bcbickers]

The 5K ultrafine is pretty good now. Even the 4K. The issues HAVE been fixed. They are easy to find second hand, however just make sure you have the one that does not have the wi fi issue (the first iteration of the 5k Ultrafine). Do not buy it new if you can avoid it. If that is out of your price range go for the Dell 27 inch 4K monitor or the new Microsoft HDR monitor (1440P). Yoy should be fine!

I am actually am shopping for something to replace my two 22" Acer 1080p screens and am seriously considering the 27" 5K Ultrafine for its screen quality and single-cable solution. But I noticed you mention not to buy it new. Is there a reason to avoid a new unit and buy used, other than price?