If used properly, the AFG's are very comfortable for a lot of people I shoot with. If you shoot your gun with your stock fully collapsed, you probably won't have enough rail space to get the AFG out there where it's intended to be unless you have very short arms.

When using an AFG the way it is intended to be used, your left arm (if right handed) should be pointing straight out with your elbow locked or almost locked. If you mount it further back you have to bend your wrist in an uncomfortable way, or choke up on the AFG.