I have a very nice vintage C-90, the black tube one, with the better coatings. It has .965 accessories, which is not a problem with me. The newer ones have 1.25 accessories. The new ones are cheap, you can get one for around $150 with a backpack. Some differences also would be the focusing mechanism, with the vintage one being focused by turning the front part of the OTA, while the newer ones use the more common focus knob at the back.
The vintage ones sold around $450 to $500, depending where you got them at. So I would say that the newer ones are quite a good buy, because I have heard that the optics are pretty darn good. I would think that the 45 degree diagonal would be one drawback.
I really like my old one, have thought maybe about getting a newer one since they are so cheap, but the views would have to be a lot better for me to do that. Mine was made in Japan, and I purchased some nice Japan made .965 eyepieces for it.
Just for common knowledge, if anyone has used both of these, is there really that much difference in the views. Remember, I have no problem with the .965 eyepieces, since they are all quality Japan made. And with my 90 ETX, I have two nice examples of a 90 mak, I just like this size scope for ease of use, especially since I have passed the big 70 year mark.