Some of them could be badly designed. Mine has a part that hooks over the top of the door-frame, along with a bar that sits against the door frame on the other side... so the more weight you have on it, the more solidly it sits. I like that my body weight isn't hanging from a little screw in the door frame (which I suspect is a failure point).

From what I've seen in those videos, most of the time people are screwing around, swinging out of them and trying to do tricks... if you're doing proper form when the bar breaks, you should probably be landing on your feet anyway?

I'd definitely recommend getting one though.