I have a HK USP .45 compact.  Im basically trying to move most of my firearms over to RMR because YouTube says so.

WOULD you slide cut your HK USP?  If yes, how would you do it, and with what optic?

I am inclined to leave this gun stock since its kidn of a classic, and just keep my eye out for a Glock 19, since there ar eso many slide options there.

I also have a Sig 220 I have the same conundrum with.

I too would be inclined to leave it as is.  Glocks, Sig P320s, VP9s and a bunch of other pistols are a dime a dozen (at any time other than a COVID panic and an election year) uncut and are also available RMR ready.

I did question this at the same time.
To test it, I just ordered a dovetail mount plate with a cheap red dot to try it out.
If I like it, I'm going to buy another slide and then have it milled for one.

I'd like the trijicon sro,  but my wallet says no.
So it'll either be the sig copy of it or a holosun 507