I bought one recently on the cheap and when I got it, the rangefinder was misaligned both horizontally and vertically. The screwdrivers were soon out and after opening it and looking at its internals, I manage to align it correctly (in the end).
However: the rangefinder system on this one is pretty different from the standard rangefinders. The moving image is created by a prism, which is right behind the viewfinder front window; this is the window that is aligned with the window at the back through which you look at when composing. When you rotate the focusing ring, the prism is moved horizontally in front of the viewfinder window and thus shifts/alters the main image. In this camera, the double image (i.e. the one that is coming from the secondary window via the internal mirror in the rangefinder) is fixed and not altered at all as you move focus (even though I think it also goes through a prism lens in the rangefinder).
Altering the main image via a prism has a serious shortcoming: it depends on the relative angle you look at the image through the prism. If you eye is 100% aligned with the axis of the prism lens, then you are fine (as long as you can stay that way). But if you move your look and your eye is no longer aligned with the axis of the prism lens, then what you see depends on the relative angle between your eye and the axis of the prism lens. In essence, moving (or tilting) your look through the viewfinder will alter the image you see and on which you base your focus.
In practice, here is a manifestation of this odd design: set the focus to infinity and look through the viewfinder at an object far away (preferably in daylight). Move the relative position of your eye to the viewfinder (e.g. try to "tilt" your look) and you will see that the double image is moving as you change the angle of your look. All that without even moving the focusing ring.
The other thing to note is that the focusing arc from the minimum distance (=1m) to infinity is around 50º. It is very small. Hence, one small rotating move on the focusing ring can take you meters away in the focusing scale. I have tried focusing at an object which is around 3m away, and I got a distance on the focusing ring ranging from 1.5 to 5m, depending on how I was looking through the viewfinder. Not impressive at all.
Bottomline, I don't think that this rangefinder is designed for accurate focusing. You are looking at a curved image through the viewfinder, and hence its position in the viewfinder window depends on the angle of your look. The small deviations (or errors) as a result of that can be very significant if you shoot near distances and wide open and probably minor or insignificant when you shoot in daylight.
Other than that, I like this little thing. The viewfinder is bright and contrasty and the controls are dead simple. The only plastic parts i encountered were mostly external: the Auto/Bulb/Flash ring, the mount directly inside the focusing ring and a few small levers further inside (the actual focusing ring is metal even though it looks plastic). The rest is metal, e.g. the lens construct, the focusing helicoid, the mount for the focusing helicoid, the top and bottom covers and the film transport lever. I cannot see serious stress on any of these components (especially the plastic ones), so if you get yours cleaned up and lubricated, they (and the camera) should last for a long time.
I'm now ready for some film, in order to check this Sonnar optic.
