While it's always nice to have new techniques to put into your toolbag (or man-bag, for some of the other members here
), I would say that if you're going to be kicking like that, you may as well just go for the nuts, or stomp a knee. Like NDD was getting at, yeah, it could be a good technique with lots and lots of practice and some luck; but for the down and dirty, why risk missing and just giving the guy a charlie horse? I've seen a whole lot more people go down from getting kicked in the junk than from femoral shock.