All the "Universal Finders" from the FSU will work just fine on top of a Leica, however the ones designed for the Kiev (Contax) style camera extend out over the shutter speed dial on a Leica and may make setting the shutter speeds difficult. They are all identical optically, and offer a fairly good view, even with glasses.
In other words, there is only one base design, however they are made so the large circular ring that contains the different objective lenses either extend laterally out to the left or the right of center, when looking at them from the back of the camera. If you want the most convenience in use, you need choose one that extends to the left, not blocking the shutter speed dial of the Leica or Fed or Zorki clone. For the Kiev, since the shutter speeds are set with a ring around the film advance knob, one would think that either type would work fine, and indeed they will, but the one designed for the Kiev takes into account the difference in height from the center of the camera lens to the center of the viewfinder objective, thus delivering a more accurate view of what you are shooting with a Kiev.
While giving a good view, these are not built to the accuracy of the finders available currently, and you may find some discrepencies between finders in their view in relation to what the lens sees. Best to compose loosely.
