I've been put to sleep with it and also won matches in live competition with it. We have been playing with this choke at the yooper hotbox for a few months and its deadly.
Luckily I was there with Greg when Red showed this one to us, and I love it a lot too.
We have had mostly success with using it from bottom when in side or in top side. And you can go from one to the other (roll with their momentum if they try to roll out.)
If the guy is on top and mounts, its still on unless he defends the elbow.
Red was mentioning that his guy's let opponents pass their guard to fall right into it.
I personally like it from top quarter guard too, but have not felt the right angle in full guard from the bottom to try it.