The Black Diamond Magnetron Gridlock is essentially a regular Gridlock HMS carabiner with the exception of its unique new locking mechanism, featuring Black Diamond's Magnetron Technology.
Black Diamond's Magnetron locking mechanism utilises magnets rather than springs to lock the carabiner shut. Black Diamond claim this makes the carabiner both safer and neater than counterpart spring or twist locking systems… although they don't entirely explain why. Whilst it obviously has the advantage of locking automatically on closure (as per any other spring locking mechanism), some have also suggested it may be better for use in winter conditions, being less likely to freeze up.
The Black Diamond Gridlock HMS itself is a hot forged I-beam carabiner which cleverly traps your harnesses belay loop via an inbuilt protrudence as part of the gate, to eliminate cross-loading.
In our view Gridlock style carabiners are a good idea, and well worthy of consideration as a belay carabiner.