After thinking about it a bit it seems like maybe it wouldn't be that great of an advantage heel hooking. Once your foot starts to slide it seems unlikely that the next ridge of rubber will really stop your foot from skidding off the hold.
But who knows (someone here?).
Let's assume they work, here's the question:
Should they be legal in comps?
What if someone claimed a FFA using these to heel hook the crux? Legit? I don't think so.