I had a case of “trackball thumb” that pained me for years. I went to myofascial therapy to deal with a shoulder that also pained me for years — enough to drive me to therapy. Shoulder took 3 treatments. At one session, I asked to have the thumb looked at. Thumb took 10 minutes — an astounding result. Pain gone.
YMMV but as the software engineer said: “It works for me.”
I've been using Microsoft's (long discontinued) Trackball Explorer and it's fantastically comfortable to use. The ball gets rolled with the fingers and the thumb does the right-click and scroll wheel.
I've laid in spares for the inevitable time when this one dies.
YMMV but as the software engineer said: “It works for me.”