If you're referring to the 1950s one, it's very nice. Physically it looks like the Summitar but the difference is that it has 10 aperture blades and uses 39mm screw on filters. Clean ones are easier to find at reasonable prices since it's not talked up in forums unlike the later Summicron Rigid and DR. People in forums keep repeating that the collapsible is not so sharp wide open blahX3.
A sharp, clean, and fog free Rigid or DR will likely cost twice as much as the collapsible.
The lens produces ellipical highlights. The oof area is very smooth if the subject to background distance is 2x or more than camera to subject distance.
Btw, mine is a screwmount.
Buy one and shoot with it, you'll like it. If not, you can still sell and not lose money.