Comment by boothby
I'm prone to RSI, and I started using a logitech trackman in '99 or '00. I've occasionally had periods of using mice or trackpads, and extended use of either causes flareups. I've never had flareups with a thumb ball, even with pointer-intensive use like CAD, FPS and graphics. So I keep returning to them -- I've been using them more or less continually for around 25 years. So for my body, it's a clear win on ergonomics; ymmv.
I can second this. Same story, been thumbing it for 25 years or so. I've also used it through some fairly painful ligament injury ('gamekeeper's thumb'), and if anything I think it helped with the recovery.
I remember someone telling me 20ish years ago that, as opposable thumbers, we have more nerves/muscles dedicated to each thumb than we do for the other 4 fingers combined. Not sure how true that is, but it stuck with me.