demos like that would give novices alot of confidence that you can do alot of damage with Hapkido, which seems to be the priority of many people when assessing potential martial arts. I enjoyed the demo but I certainly hope those uke's (or whatever they're called in Korean) warmed up properly. That master looked like he hyperextended a few of those arm locks. However, I was uncomfortable with the severity of the demo when the uke was clearly compliant. Pain can be the objective of the art without you having to prove it against a compliant uke. Aiki-Jujutsu uses alot of pain compliance in its techniques but the objective is control not damage (though damage can be a real consequence).
Trust me - it doesn't really hurt. They are just screaming and flapping about for the demo - they are very good at what they do but my take on demos like that - PATHETIC. It's like pro wrestling. They don't normally train like that though - it's more for the demos. At least, where I trained in Hapkido they didn't. If you can't see thru it you need to retrain your eyes or you'll end up with a teacher that's no good.
PS And if someone did a technique on me that really hurt like that they would find out what I thought about it when it was my turn. Been there done that