In my opinion, based upon years of training, is that the one shot stop concept is complete BS, compounded by sheer stupidity.
If your life is in imminent danger, only a fool would rely on one shot to end the threat. If you are forced to resort to deadly force, the only object is to stop the attacker from continuing the action that is a threat to your life. In order to do this, you will be forced to continue to fire until the threat has ended. If you are justified to fire one shot, you are just as justified to fire as many as needed to end the threat.
We were taught to continue firing until the threat has ended. Subject on the ground and unable to continue to threaten your life, or running for the hills. I, for one, would never count on one shot to accomplish this.
Therefore, I think that a "one magazine or cylinder" stop, is much more realistic.
Just my opinion, and you have paid me exactly what it's worth.
God Bless America