User Review: Black Diamond ATC-Guide
I've used many different belay devices, and this is the best. It's intuitive like the ATC and other similar belay devices but this one is special because of its many other features, the best being the ridges on one side that offer more friction. The other two loops on it act similarly to the Reverso by Petzl so you can belay from your anchor instead of your harness, but when you have it set up this way the ATC-XP Guide becomes a self-locking belay device. That last little hole is used to tie some webbing through it and the carabiner because when it self-locks, you'll need the leverage to unlock it.
So overall I believe this ATC makes all other tube style belay devices obsolete because it's intuitive, versatile and smooth.