The R6 uses an electric shutter, and it seems that shutter release is not instantaneous. The R6.2 has a mechanical shutter, but it also has a hefty price tag. But I think it is the best of all the Leica SLR cameras.
Both the R6 and the R6.2 have mechanical shutters and no automated electronic modes. The batteries only power the light meter in both these models. The 6.2 adds a 1/2000 shutter speed and some other changes.