FWIW, I had pain and sensetivity in my thumb joint (mostly right hand, but also with the left thumb too). I thought it was a result of interacting with the screen on my phones over the years. I was never in significant pain (unless I jammed my thumb), but after using the TextBlade for awhile, I realized that I no longer had thumb pain.
It is possible that my pain was a result of interacting with my phone screen, but I don’t think I have decreased my phone use significantly (although I do less on-screen typing). I suspect that my thumb pain was RSI from keyboarding and that the TextBlade has addressed that pain.