The best exercise, for myself, for the "RSI" (tendinosis most likely) in my right forearm is archery with recurve and longbow in particular, not so much with compound.

Any pain I have in it is halved, and it feels much looser and stretched out. And as a bonus my medium distance vision also gets a workout.

I bought a power tower for chinups and pullups earlier this year but unfortunately it contributed to aggravating both my elbows and forearm.