Depending on the style, some don't lend themselves to being ambidextrous, if that matters to you. I'm left handed and my cousin has a rh boyds thumbhole, and while I can shoot it well, it's not comfortable at all.
Depending on your shooting style, they may force too much contact with the rifle. When I shoot prone, my hand is barely on the side of the grip. But, if you hunt timber or thicker cover where close/quick shots may happen, they are tops in my opinion for off hand work.