Around 10yrs ago I started developing RSI in my right hand, I guess partly because of the mouse scroll wheel, so I started mousing mainly with my left hand, but switched back and forth if that was more comfortable. While it solved the main problem, still didn’t feel as comfortable as I wanted. Now I have the perfect solution: standing desk, mechanical TKL-keyboard, and two trackballs on each side. I wish Logitech made left-handed trackballs, but the left-handed Elecom wireless feels okay and looks similar to the MX Ergo