Carabiners are the glue that holds the climbing world together, and you can never really have enough of them in your kit. Black Diamond has always made stellar biners, and with the introduction of their Magnetron technology - available in the VaporLock, RockLock and GridLock models - one-handed locking and unlocking has never been easier.
We've always loved the VaporLock for its light weight, pear shape - effective for increasing friction on belays - and general all-around utility, including the ability to effectively work a Munter hitch on ropes up to 9.4mm. For those reasons it's been our go-to biner on three trips up Denali. Last time up we tested the Magnetron locking system on the RockLock and GridLock and found it to work great, even in subzero icing conditions.
The Magnetron VaporLock is only a fraction of an ounce heavier than the screwgate model - 2oz versus 1.8oz - and otherwise nearly identical. Both models have large gates to accomodate their respective locking mechanisms, and the nose profile on the Magnetron is slightly larger to house the steel inserts for the magnets to grab onto, but you won't notice that on your rack. What you will notice is the ease of use, resistance to snagging thanks to the keylock nose, and large 20mm gate opening. If you're only rocking one locker on your rack, the Magnetron VaporLock is the way to go.