Just my opinon, but I think he might be better off with a chest or shoulder holster. Both hands are probably busy, but having the gun closer to hand level (pretend you are a barber for a minute) might make drawing easier. It also leaves it closer to your hands should someone try to take it. Hopefully he gave some thought to it, or will practice with it in the near future.
Interesting thing though, I've spoken with several local gun store owners, all of which open carry while behind the counter. They have never had anyone try to rob them. Attempted burglary yes, but never robbery. Open carry definitely deters crime.