A "rubber dome" or membrane keyboard requires the typer to press the dome all the way down to trigger the key press. On a mechanical keyboard, it is a mechanical switch to trigger the keypress. On Cherry MX blacks greens and reds, there is no feedback when you have pressed the key. However on a blue or a brown there is a tactile "bump" when the press is registered. Critically this happens before the key "bottoms out" or hits the bottom of the switch groove, so you can release the key before that second strike occurs on your fingertip. With the blues, the "activation point" as it's called makes a loud click as well as the tactile bump, so as you get used to typing on them, you'll release right after the click.
I'm not sure of the effects of mechanical keyboards with regard to RSI, but if you're a hard typer, they might help train your hands to not bottom out the keys.
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