DMM - Belay Master 2
The DMM Belay Master 2 is an awesome tool that we really like. First of all it is a super light carabiner with high norms. It can be used with the plastic clip on during belay work or with out it will function as a normal carabiner.
During partner checks it will be easy to see if the belayer has closed the screw lock as it is only possible to clip the plastic down if the screw lock is closed.
The plastic clip ensures that the carabiner always stays straight during belay situations and takes away the potential for the carabiner to flip into a bad alignment and for cross loading to occur.