Pros: Great sound.
I have mine and it's fabulous. I imagine especially good for harder to drive cans. Better bass, not just more bass, but tighter and better defined. Better 'air' around the instruments, ie, improved separation. Maybe some golden-eared individuals will do a better review. One poster described sibilance and I definitely do not find that with my setup. I used it with my Cowon x7 and the Shure SRH-940, comparing with and without using the outboard amp. This combination has superb synergy. One needs to spend a heap more money to get even more realism from a setup. ( I should add the the Cowon does a great job driving these cans all on it's own, but it's simply better with the amp). As always, YMMV.