I was the IT Director for a company that had a lot of data entry people. I had noticed that the keyboards that they were using were mostly plane jane, mismatched, membrane keyboards. After a bit of back and forth with purchasing I convinced the company to purchase a ton of mechanical (cherry reds), split ergonomic keyboards.

Within a month RSI reports were down by 95% and after 2 months were essentially nonexistent. I also noticed that people had stopped wearing wrist braces as well. I paired this with good, well shaped mice that would hopefully lead to less fatigue with repetitive motion.

My sample size is tiny, but there are 30 some odd people who if asked, would back me up on this. So while not thoroughly scientifically proven, I am willing to say that ergonomic keyboards do make a big difference. I think mechanical makes a pretty big difference too. Cherry reds activate with very little pressure and, imo, make typing long documents or notes much less annoying/stressful/painful/