I have one with the eyes for my M3, if you have an M3 you will need the eyes in order to focus it properly, I learned from experience. I bought it for the same reason, it was cheap but mine is very clean, it performs well beyond f5.6, it gets alittle "muddy" from 3.5 to 5.6, for about 275-350 bucks (maybe cheaper) you should be able to get the newer 35/2.8 summaron which is reported to be close to 35/2 summicron quality, here are some samples from my 35/3.5 summaron:
Todd