Where is the muzzle pointed when holstering/unholstering? That direction alone makes a negligent discharge more likely to hit someone, namely, yourself. Note the location of your femoral artery. Training instructors not wanting students they don't know in a position where this is the case makes sense. That's all I'm saying. I'm guessing that is probably there logic in restricting the use of them.
Shoulder holsters certainly can be just as dangerous if there are people standing behind them.
Shoulder holsters certainly can be just as dangerous if there are people standing behind them.