Make sure the picture is crisp and colorful. Remote is a plus. I assume it has component video? It's difficult to tell from the pics. I used to use an RGB Scart converter to Component into a Trinitron and found it to be quite nice.
I was always curious how much more quality you get from a setup like that. Seems the most popular CRT setup with RGB is on BVM/PVM's.
Well sure, a professional monitor cost 5-10x a Trinitron when it was new. So, of course, it is going to have a better picture. The PVM/BVM also has a lot of control over the geometry of the picture. On the other hand, consumer sets are able to get much brighter, making them more suited to playing in a brightly lit room.
As for the RGB vs YPbPr quality, it's hardly noticeable. However, the difference between YPbPr and composite is huge and looks great on a CRT.
If I had to start a setup now, I'd go the with Trinitron and RGB to component converter. Plus, you don't have to pay $1k for something bigger than 20".