Does Leica L39 mount work - and how well -
I have a no-name M mount adapter and then the M39 insert that goes in it
Tried an old collapsible 50mm (M39) and a summilux and... pretty much hated manual focusing experience on XPro1. And the fully manual aperture is not fun either.
Manual aperture is how rangefinder and tilt shift lenses work. If the focusing mechanism is external, it works great. If the focusing mechanism uses TTL mechanisms, it isn't that great. It's a shame the X doesn't have a good way to focus manual lenses using the OVF, but even if it did, the system would be TTL and make it harder to focus unless the lens was wide open.
That is the reason the X lenses are SLR style. In order to focus, TTL, the lens must be held open to focus, and then close down for exposure (if not exposed wide open).