Membrane keyboards are the same as rubber dome keyboard. Same thing, different name.
The main difference between dome and mech is that, unlike domes, mech keyboards don't bottom out the key no matter what you do. In mechs, the key needs to be pushed all the way down in order to 'bottom out', but the key is registered when pressed down half way.
Different people report different things when it comes to gameplay. The switch to one didn't help me at all, it was just a better overall experience especially when streaming.
Others say that a mech helped their accuracy etc.
(Plus, a mech is just a better investment. They don't break as easily if you get a well-built one)