Zero
Master Black Belt
Seasoned, this is interesting and I note Haze states the same, I think. In my Okinawan goju club, we have always trained the high knee chambered front snap kick. I have only rarely competed in sport/point karate but this (coupled with alternating hook kick - same leg) is one of my most utilised kicks in full contact open karate tournaments and also kickboxing competitions. Our sensei, taught us this from pretty much day one.This kick is not taught in Okinawan GoJu, but is good for point sparring.
We use it much like the jab, as granted, the other version described above, while slower and more telegraphed, when used in combinations and with timing is the more powerful for knockouts - much like traditional muay thai shin attack off back leg; it's the one you use when the opponent is set up or your timing is beautiful.
The great thing with the high knee front snap kick that comes straight up is that you can mix the same kicking leg with the hook kick to the other side of the head/jaw to catch opponent off guard. If you want to risk keeping just one foot on the ground that bit longer you can do this without even dropping you leg (I used to train this a lot after watching it in movies but never tried it in competition(!)). Also the front kick is often hard to see coming when mixed in with punches and then stepping just out of punching range as it comes right up the centre line and then the foot or shin comes in from the side, beautiful kick....I know you know all this, more for the benefit of the others progressing so they don't just stick or revert solely to the "more traditional"(?) hip/pelvis swinging motion, which is not as fast.
Anyway, all I meant to say was that, we havedone this in our curriculum and my sensei would have used this circa 30 years (although I recal way back he did a training session with Bill Wallace), so maybe this is where this kick has come into our style if you feel this "ain't legit" Okinawan....
Best