I understand you find a concept and want to question where others do or don't do it.

For one thing, many of us would not answer such a question if someone came into our schools 'demanding' an answer. Most systems have an internal order to instruction, waiting till the students abilities rise to the level of the technique.

The movement you're qestioning might have severe reprecussions is used, but then there are any number of techniques that can do the same, hurt someone badly.

Off hand I can think of a number of karate systems that use that technique openly in their instruction, at the appropriate level, and I'm quite sure there are others that do so more privately. Or you can go outside of karate into a system like the Bando Boar that uses the same technique.

Let's suppose that I might do so in the Isshinryu I teach, on the assumption that the Isshinryu hand stiking formation lends itself to such a use, that instruction would not happen till well after the student is in their black belt studies, and only as a minor variation usage of the vertical striking fist.

There are various reasons why it is not taught earlier, but the most appropriate one is in our current local there is absolutely no need to address it differently. Other times and places I might reconsider that answer.

The technique is neither more or less effective than many other techniques.

My answer of course is only theoretical, especially as I'm not looking for students, nor choosing to give away the manner in which we instruct.

Truthfully, if you want real answers, you have to wait till you can begin serious study, and then find them out in time.
victor smith bushi no te isshinryu offering free instruction for 30 years