This thing is super. When it comes to the belaying function it really does lock up like a camming device (gri gri). On super thin ropes it may slip allitle but fine if you are always have your brake hand on. The 10.5 mm rope i generaly use however lock up on falls 99.99% of the time. It locks up good enough that it would easily stop a fall with the brake hand off the rope. (not that you should every do this). The only downfall is its limited function, belaying the leader, but it does it very well.