I would definately give that moldable mouse a try, providing the fabric on it didn't resemble that stuff covering the wrist rest on my old mouse pad. (it would have been soft & comfortable for most people but for some reason it damaged my skin)
I like the idea of how it can be reshaped as often as needed, into whatever is currently comfortable for the user.
The only bad thing I can see, is how it will serve as a fantastic 'fuss toy' for people that like to fiddle with things instead of getting work done. It would give them something else to play with all day.