I was having wrist pain from using the mouse, and switched to a trackball, issue solved, if the wrist doesn't move/flex, it doesn't get strained, therefore no pain.

The only thing that moves is my thumb, and it's much better for flexing than the wrist, also it has a tiny load to manage vs the wrist.

I did the same, though to non-thumb trackball (CST2545), which I find also virtually eliminates wrist stress.