I purchased this belay device even though I already own the Black Diamond APC Belay Device. While the APC is a great model that belays smoothly, I wanted something with a little extra bite for those times when I'm lead climbing and my girlfriend is belaying.
Well, it works great! With the ribbed side facing your brake hand, the rope stops instantly with little effort on your part. If you're looking for smoother rope flow, you can flip the device so that the ribbed side is away from your brake hand. In this position it acts similar to the ATC.
Personally, I think it's worth the extra couple of bucks to get this model over the ATC, although they're both great devices.