Your best defence is a good offence. This is a very good tactic. The reality is we have to consider the legality of each situation we encounter. Each country will have different laws reguarding self-defence.
In Canada a person has the right to defend them self if they feel a personal assault is imminent. A person has the right to deffer the violence if they feel the attack is imminent. This means I feel the person in front of me is about to cause me bodily harm, ( they show all the physical cues ie. threatining posture, clenched fists, agressive, verbally abusive) at this point the threat is imminent, and one is able to use a reasonable amount of force to prevent the assault. The strike you mentioned would be an effective way of deffer the violence. There are other factors involved as well.
One does not have to wait to be a victim before they take action. This is a responsability. If a martial arts instructor teaches, but does not share the legal aspect of self-defence with his students, he/she is setting them up for failure and possible incarceration (prison).
One should explain the legal aspects of self-defence to their students. If you instruct martial arts, but don't cover the legalities, you should learn and research what you are teaching to your students. After all, law-suits aren't much fun...........If You teach your students how to respond, it is your respond-sibility as an instructor to educate your students about the law.
This type of striking method can be seen as covert, and a very quick response to prevent violence. In the real world a person may have their hands at their sides. It is at this point that agressive person may attemt to take advantage. You just don't allow them the chance. Martial arts goes beyond just the physical response. There is the Mental, emotional, spiritual, and legal ...
Troy/Canada