I haven't tried the APO yet, but have tried my f/4 Tele-Elmar. Focuses fine - or at least as well as on any .68-.72x Leica body. The magnifier would be a good accesory (for some reason I find the magnifier less uncomfortable on the M8 - less tunnel vision effect. I guess because the view is a touch wider to begin with).
There is no framing in the viewfinder for the 135, but the image area is essentially twice as long and twice as tall as the rangefinder patch, so it becomes fairly easy to learn to aim the camera with a bit of practice.
The coding is essentially meaningless - especially for a lens that long (far from the sensor). No vignetting to correct, and no color fringing with an APO lens.
Both these 135s LUV digital sensors. They produced astounding detail on my Epson R-D1 - when I could get them in focus (shorter RF base).