I believe that the technique, fished in the right type of water, may be more important than the specific fly that is used.
It seems to be best when fished in a moderate current flow where the water is approx. 1 to 4 feet deep. It is even better when the bottom has rocks, big and or small, on the bottom.
He often fishes a variant Prince Nymph, with dark brown dyed partridge, but I've seen when a large fly with just a medium olive dubbed body and a partridge hackle worked just as well.
I guess you can call these flies whatever you wish, but I call it fun.