This is a very unique and extremely rare lens. I saw it only once up for auction on eBay in Germany. The starting bid was at 200.- Euros, and the auction ended at over 350.- Euros. This lens can only be used on M42 cameras which allow the mirror to be flipped up manually (not in combination with a self timer like the new Voigtländer Bessaflex TM). The mirror needs to be flipped up before you mount the lens on the camera.
The rear element almost touches the film, and the lens is - once mounted on the camera - small like a Carl Zeiss Tessar 45 mm 1:2.8 “pancake” lens for the Contax/Yashica mount. The lens also comes with its own viewfinder which can be mounted on the hot-shoe of the camera (as known from rangefinder cameras).