I am a huge fan of orientation-limiting biners for belay device connection - either onto my harness or directly off the belay! Besides the ergonomic help in always having your belay device in the same space/place meaning you do not need to look at it, nor do you need to keep ensuring correct orientation/loading, as with the knot on the climber's harness, this is the single connection point and deserves to have as much redundancy / correct usage as possible without human interference.
The correct usage of these orientation-limiting locking 'biners is the narrower end (the end with the internal wire) attached to the belay-loop or belay anchor and the pear nose of the 'biner for the device.
When belaying off your harness in this manner, the 'biner is often vertically aligned. This means that the locking barrel on a screw gate locker is at risk of unscrewing because gravity is pulling it downward, and active belaying can sometimes cause the barrel to "shake down/loose"
The Belay Master plastic locator prevents this, as well as ensures that the biner cannot pivot around the belay loop, causing cross-loading.
Also, you *know* that your device is locked when the gate closes because the plastic cover will not close with the locking barrel 'down'!
