Just went back to my copy of the Krenzel book.
The two techniques are different. Ken uses his left thumb to push the block. The action is the same as a standard block push-off, but the block is traveling over your empty hand, rather than traveling over the final card of the bunch that you're counting. There is the possibility that the block will spread.
My technique uses the left index finger. The block travels in a slightly different direction but this is compensated for by twisting the left hand at the wrist. Not only is the move dead easy, but it can be done during a very rapid count and there is no chance for the block to spread.
I use this move every night that I do magic; it continues to fly by laymen and magicians.