I temporarily lost the use of my right hand from an injury, and found the Magic Trackpad (for a Mac) just as easy to use with my left hand as my right hand, and now still use it with either hand. However, if that person has never used a trackpad it might be more challenging to learn, aside from the other challenges involved.
btw, the Apple Magic Trackpad for Macs is far superior to any other trackpads for PCs, which in my experience have been frustrating in comparison.