Great for belaying a lead climber. Feeding rope out is a breeze compared to other devices. Easy to use. Quick rope grab. Very safe process with minimal training. Very minimal wear on your rope.
Even though it is clearly marked wich way the rope goes... setting up the rig went against my instinct of how it should work. It took a minute to re-train my brain.
I have a collection of belay devices and have tried them all. This is the only one I use for sport or TR. Much easier and safer to belay leader than gri gri. Excellent for belaying someone working a difficult route. It loves catching falls over and over. Simple to rig and easy on ropes. Great on skinnier ropes (9.1-10)
Slightly heaver than a gri gri, but if you are gonna haul a gri gri, this is worth its extra weight. It also takes a little practice to lower/rap. I believe it is rated 9.1-10.5mm, but anything over a 10.1 is a little bit tougher to feed lead.
I wouldn't use this for trad, unless you are really careful. I have 6 different "auto-locking" belay devices and 4 of them sit in a box in my climbing room (the wife has the gri gri on her harness). As far as they go, this is the way to go!