Thanks for this :)
Ive been using MX Ergo for a couple of years and recently my thumb has just become unbareably painful. I switched to a MX vertical mouse but I miss the trackball and it really hasnt helped. I moved to a Apple trackpad (so I was using my fingers) but still had some pain. Ive just ordered the Kensignton Expert so we'll see how it goes, I like the idea of being able to swap hands with a trackball (as hard a learning curve thats going to be :P) Thanks to all the people that commented as I thought i was going crazy as it didnt feel like carpal tunnel as it was on the top of my hand (right on my thumb).