Hadn't heard of it until this thread-- that being said, I had to give 'er a try..... Man! Is my pointer finger ever tired.
I googled it when you posted the thread, and tried it for about an hour this evening-- and, seriously, my pointer finger is fatigued, and the rest of my hand feels tired.
I don't know if it is the placebo effect (after reading the virtues of this grip) or if I was making a point to be more diligent in my casting stroke, but I noticed that I could form tighter loops with out crossing the line to tailing loops.... I also like that I can 'point' at my target, but my hand is going to have to get used to the 'unnatural' posture.
I do like the results after trying it out coming from the thumb on top grip.
also, I will have to get used to my middle finger being the 'line hold' or put another way, using my middle for line control.