I have the AFG on my carbine and I like it. Thing is, it's not a 100% perfect solution, it's a compromise. A vertical foregrip will allow a more natural wrist position during extended use. Also with a vertical you can pull the rifle back into your shoulder much more, which some people like.
Now for what I like about the AFG. One, it does not dig into your leg when resting on your lap riding in a vehicle. This alone sells it for me. Also how you grip the AFG is important. You should get complete purchase around the grip and rails of the rifle with your thumb extended over the bore line. This will allow you to control muzzle flip more and provides a rock solid shooting posture if used correctly. This grip will also reduce side to side wobble compared to a vertical. Finally the AFG can be used with just about any position or posture, including ones where your hand would leave a vertical grip and grab the rail instead.
If you are limited on rail space, carbine length, the AFG2 might be better. I have a specter length rail and there is plenty of room left over on the bottom rail after attaching the grip.