I just got my AA "Swiss" vertical grip Monday. It wouldn't even start to go on the Liberator II handguard rails, so I stuck it on my Fobus M44 handguards on my M4gery...it went on with not trouble.
I thought about it, and figured I was gonna get that grip on the rifle I got it for if it killed me, or the grip. I had to pound it on the rails with a rubber mallet, pound it off, file the piss out of it, pound it back on, off, file some more...but I finally got it to slide on and off with relative ease. I don't know what the problem is...all the ARMS stuff I'v tried went on and off very easy on those handguards.
The grip is kinda cheap and plastic feeling, IMHO...plus, even with small hands, I find it a little narrow, and about 1" too long.
The grip on my M4gery is the one that ACE sells...it's a little stubby one, that goes on with set screws. Not "quick release", but it does feel nice and solid. Bad news is that it WILL scratch/mar your rails, so be warned.
That grip from Global Tactical looks pretty good...I might have tried it had I seen this post a little sooner.