The one I have is pretty strong, it hasn't budged an inch despite all the pullups I have been subjecting it to. You got to really bend your legs to get full ROM or else they end up dragging on the ground.
One of my mates decided to show off on it once, being the amateur crossfitter that she is, did one kipping pullup on it and promptly smacked her face right onto the doorframe above. I never laughed at someones expense so loudly/rudely in my life.