Wayne C.wrote a review of Petzl William Locking Carabiner on June 6, 2011
Triact is a bit cumbersome for belaying, but verrrry good for setting up anchors, abseils and top ropes
I also got the triact for its security. The gate slams shut with a satisfying clink, because of the strong spring, but can sometimes remain ajar if you don't let it shut wih enough force.
It's possible to open the triact gate with one hand, which leaves the other hand free for rope/belay devices. However, I find it a bit cumbersome for normal belaying.
However, it's really useful for setting up anchors, abseils and top ropes outdoors, because you can be confident that the gate isn't going to open.