My understanding is that the Jupiter-12 won't mount safely on the CV cameras.
I just looked at this question myself, vacillating between a collapsible Summicron and a Nikkor 50/2. I ended up with the Nikkor and am quite happy with the couple of "smoke test" rolls I've shot so far. The collapsible Summicron that I didn't buy is still there at KEH (although I've read that it probably won't collapse on the Bessa-R, which is the same body I was buying for).
This seems like it's kind of an "embarrassment of riches" situation; there are a *lot* of good screwmount lenses in the normal-to-slightly-wide range.