>The problem with your fingers is that ALL of the tendons that move them pass through the carpal tunnel
CTS is down to wrist posture not finger use - musicians rarely get carpel tunnel syndrome despite many 10Ks of hours of intense finger use, as correct wrist posture is taught (or learned though pain) early.
With the old logitech (RB-22?) and current Elecom's your thumb is still working hard (clicking, holding clicks etc) whilst fingers barely move. The thumb ball designs still require your fingers to handle clicks, hold downs so it doesn't get you off the CTS hook if your wrist is unsupported or raised.
Thumbs are pretty poor at precision generally (even simple linear movement on a surface requires rotation and both joints bending) it's why we paint with our fingers not our thumbs.
