Here's what other sites are saying:
Climbers could argue whether the HMS 3Lock Carabiner is Camp USA's safest locking carabiner all day. Technically every Camp Carabiner is certifiably safe, but this is an auto-locker with three separate actions required to unlock it. This certainly adds a sense of security when you're belaying a buddy, to you and the climber.
C.A.M.P. Accessory Biners Hms 3Lock Carabiner Blue 118403. This is the best choice when using an auto-locking carabiner to belay.
The Camp USA HMS 3Lock Carabiner is an automatic locking carabiner for the belay or rappel. Safety is pretty important while Climbing, so why not add a 3-action carabiner to your equipment? This Fits in and is usable with just one hand, but requires a slide, twist and pull to open up. The more action required, the safer it is, since you know this won't be popping open on its own. At the very least it'll give those fingers and thumb of yours something to do. Every so often. Features of the Camp USA HMS 3Lock Carabiner Automatic lock requires three actions (slide, twist, and pull) to open Easy to operate with one hand Large opening and keylock nose make clipping ropes and webbing easy Available polished or blue