This device is amazing. Although, I want to make something clear. THIS DEVICE DOES NOT AUTO-LOCK. Mammut designed the device to have rope slip to make a more dynamic belay. The device works by pinching the rope between the carabiner and the device. The amount of pinch on the rope can also depend on the carabiner used (use an HMS carabiner only). I would call this an assisted belay device. It helps you catch the fall and makes it more dynamic for a smooth fall. I choose this over any other device for leading. It's light, works on skinny ropes (I use a 9.4mm rope), not mechanical, easy to use, and did I say light. #1 rule with any belay device ... keep your hand on the brake strand ALWAYS.