I just installed mine I got from Army issue. (thanks man) It doesn't seem to affect the slide/cycling at all however there are slight quarks with it.
Depending on which M9 you have, I got the elite IA black which has the rail and the straight grip. Kinda looks like the vertec but full metal.
anyways on mine, the grips are straight. However the hogues are slightly round at the bottom bit and the hogues kinda poke out at the back and pinches your palm slightly, it's not perfectly flush with the straight part of the grip. If you dont mind it it's fine, but to get it perfectly flush with the grip you may have to cut part of the rubber off.
That said it's only a very slight misfit and probably wont bother most of you. but just know that it's not perfect at the back. Ill try and get pics later. And they are pretty sweet to hold. Makes the KJ m9 feel all classy with all metal and rubber.
Another thing is it tightens the mag release button a little bit. I think it's because it rubs against the rubber and creates a bit more friction. Not a big issue. still works perfectly but not as clicky.