OK, alpha-gear-geeks, your carabiner has arrived. Designed to be used with the Petzl Grigri (but just as effective with any belay device), the Freino belay carabiner is a 3 ounce autolocking unit that has a secondary gate and basket - yes, you may call it a spur to establish techno-superiority - that provides additional braking.
The braking function is particularly valuable with a light belayer and heavy climber, making the whole process safer and smoother. Even partners of similar weights can benefit from the extra friction if they're using skinny ropes.
The Freino can even be rigged off the anchor to redirect the rope for lowering. The downside to all this increased functionality? Price. You be the judge.