Currahee's post really nails it. If you get an AFG out toward the end of a 9+ inch rail, and use a grip where your thumb is over the top of the rail or nearly so (so-called C-clamp grip), then an AFG is really good.
On the other hand, if you use it like the bottom picture in his post, as if it is some kind of independent slanted pistol grip, as opposed to a gap-filler that integrates with the forearm, you probably won't like it. You also probably won't like it if you have a short rail or try to mount it crowded up against the mag well. Your wrist will be at an awkward angle. If you like a "traditional" grip where your support hand actually "supports" the rifle by cradling it, an AFG isn't going to work for you. It will just be in the way.
It's designed for a specific type of grip/stance, which requires it to be mounted in a fairly specific location on a rail. It is a not an "alternate flavor" of VFG. It's more specialized.
I have personally found that VFG's used as thumb break style hand stops are better for shorter (8 inch or less) rails, AFG's are perfect for 9-10" rails, and some kind of simple handstop (Larue's is the best I've tried) are better for 11+ inch rails, if you likely to really stretch your support arm way out with a C-clamp style grip.
YMMV.