Excellent lightweight belay biner with some caveats
This is a really innovative biner by Petzl. It gives us a really lightweight Munter-compatible locker with a nice smooth surface for the rope to run on a standard sport/toprope belay.
But it isn't perfect. It tends to turn around very easily, meaning you'll either crossroad it or run the rope through the skinny end, with lots of unwanted friction. This is easy to recognize and address as it happens. What's harder to address is the tendency for the biner to lay "sideways" against an alpine belay device while belaying up a second, creating a ton of friction, a lot of stress on your anchor, and a general PITA. Add in some rope drag from a wandering route, and you've got yourself a recipe for some very sore hands.
But overall this biner is a huge improvement. Lightweight is the only way to go.