i have not tested any x-mount adaptors yet. but yes, adaptors to the mirrorless cameras are easier to make as there is less calibration involved, you just let the lens do the focusing and the adaptor need not move... but if cut too thick or too thin, that slight calibration error can throw the focus off at either the min or infinity focus, even for mirrorless cameras.
the example of the m to s adaptor is slightly different, yet is susceptible to the same problem. the rangefinder coupling is the added complication and need for fine calibration... regardless, when using on mirrorless camera, some can stop short of infinity, on the money, or even past infinity.
in any case, this is well off topic from the title... and if there isn't much else on the IT fair pricing (now that the IT fair is over) I'll be closing this thread soon... more discussions on the x-pro1 can continue on the other threads.