I am just back from Japan and I had a chance to play with the 21-35 finder. As with all CV finders, it is incredible bright - virtually no light loss looking through it! It is a zoom finder so you dont have the "surround" of a frame line finder. It zooms in to the focal length and shows the image against a black background instead.
It has three different scales on it. The primary one, a chrome ring" shows the focal length for 24x36mm, the second scale (cut out and white numbers against a black back ground) shows a 1,3 size (M8) and the third scale shows the 1.5 magnification of a RD -1. Sound cluttered but actually worked nicely.
Some distortion at extreme wide setting (15/18 mm) but not worse than on a dedicated finder. The foot has a screw down lock on it so that it is held down securely. Not small, but better than the Leica AM/FM radio looking thing. Oh, almost forgot - it has a built in up to +2/-2 diopter adjustment on the eyepiece too!
Before you all ask - No, I don't know the price - but even so I want one! It would make my Bessa T's very useful too.
I also had the opportunity to use the coupled 15f4.5 Heliar. Very nice package - M-mount and high build quality. Feels rock solid and a 52mm filter size justifies a miss-spent youth with Nikon F's and the lenses for that. I have a lot of those 52mm fllters to put to use once the M-mount 15f4.5 makes its way to me.