Since this thread has been revived after years of sleep, I can't resist mentioning that I just made a video on yonkyo. And I realize that I think just the same as in my comment above from ten years ago: Yonkyo is a distraction, like an atemi, and therefore it's necessary to do it shortly, as a surprise. Probably the best is if the nerve pinch is not needed at all for the technique to work. On the other hand, it's kind of fun - if not in excess
Here is my video:
https://youtu.be/nF7cxegO-oo