My only RMR piston is a FN Tactical, so it's not much of a carry gun if you want to hide it.
As for the RMR - for me, they shine at the range.
Just fooling around at home with the sight and drawing down on the TV, clock, etc, I don't notice the benefit, and if anything, it takes a bit longer to line up the dot than with irons.
But once you're shooting, just like a red dot on a rifle vs. irons, it's so much eaiser to use. You can keep both eyes open, which is hard for me as I'm not that right eye dominat so with irons I get a double vision view of the target (down the sights/not down the sights).
The dot is more precise, and easier to focus on with older eyes.
On a Glock or something smaller than my mini-Mark 23 style, FN, I'd think the RMR or similar would not add that much more size, and would really help your aim.