I have two of these on my desk and I love them. The color on the IPS panel is great. However, they are glossy so it is easy to get glare. My room is fairly dark so overall I would highly recommend them. There is also a S2240M which is a 21" display that is the same resolution. The apple display is an older technology, so if you can do without the matching aesthetics, I think that there are other current options that are a better value.
The thing about monitors is you have to pay attention to pixel density - usually in pixels per inch (PPI). A 21" iMac display that is 1920x1080 has a PPI of 102. A 27" iMac 2560x1440 is only slightly better at 109. So larger monitors have more pixels spread out over a larger area, resulting in the same pixel size, and is therefore equally noticeable if you look really closely at the screen.
You would have to get a 4k display which are still very expensive to get a desktop monitor with a higher PPI.