If you're so used to type C-x that you don't even register it, like most emacs users, then it's just pressing "r s" for "register save".

It's not terrible, and the mnemonic is sound. If you don't like it, perfectly valid opinion, you're just not made for emacs' default behavior.

I can think of no instances where I need to press a key and a modifier, a key, and then another key, in any program. If I had any bindings like that in vim I remapped them.

I'm definitely not made for emacs, specially not its pinky :)

True. The traditional binding was was just `C-x x`, but they've already done one round of making register features more inconvenient to get at.

‘Frictionless’ here means ‘we’ve done it this way forever and don’t have to think about it anymore.’