The problem is the old ones varied CONSIDERABLY from sample to sample. Some vignetted a lot, some none, some were completely blurry in the corners, others reasonably sharp across the frame. Even the viewfinder accuracy varied. A lot. Some leak light, some do not.
I have two old ones and one new one. i have not used the new one at all yet, so cannot compare, but like I said, any comparison will be useless because the old ones varied so much.
Here's some with one of my old ones:
I should try my new one.