Rafael, I have used the Hawks helicoid adapter (which I believe was the first such adapter for E-mount) extensively with the NEX-7. The manufacturing tolerances of that adapter aren't very tight at all, and it therefore has quite a bit of slop (it's pretty serious: you can see the lens move very obviously with respect to the camera when you focus or change the aperture, particularly when the helicoid is extended). I expect the Voigtländer to be better with this respect, but haven't seen it in the flesh.
I have yet to try the Hawks adapter on the A7R, and am wondering to what extent the corner performance problems with M-glass are affected by helicoid extension. In theory, the situation should improve due to the exit pupil moving away from the sensor, but there may be other factors at play, as well.
In general, though, I have decided to stay away from M-lenses with the A7R, but that's just me...