Have you ever seen how hard people can fall when sucker punched?
Yes, when I was a kid. However, I have not seen (except for TV), any violent confrontation since my youth. I guess one would have to consider his/her environment. I only go into rural bars during lunch and dinner to get food, do not drink or go anywhere where I am likely to be the victim of a crime such as you describe. So, it would seem that I might not need a retention system as much as someone who was frequently at risk because of life-style or environment.