The only device marketed as "auto Locking".
The REVO uses a centrifugal clutch, similar to your car seatbelt. Advantages include no method of over-riding the locking mechanism, during belaying, or when lowering a climber, unidirectional locking means that it can be threaded in any direction because the locking function works regardless of the rope direction.
Intuitive belaying method, which requires no changes to standard belaying technique.
Like everything, there is no 1 device that does EVERYTHING best. The downside to the Revo is that it - by design - is very difficult to "work" routes, because the locking mechanism is based on min centrifugal force/speed of the clutch, which means that a min amount of rope needs to pass through the device, to reach the braking-speed. This makes it very difficult to "take" as the climber pulls up into their highest draw.
The Revo is my go-to when guiding or instructing a 1:1 client situation because I have no idea if I can trust my belayer:
It is important to remember that, as with most brake-assisted devices, if the belayer is rendered immobile (panic/feint), and the device locks - the leader has no way of un-locking it