This amp is "off the charts good" I bought it two days ago after comparing the Fii 6 and multiple others, but these stand out as very clean and professional. As the former poster said, they increase detail with no distortion, everything is louder, more detailed, and more focused in a good way with better dynamics and cohesion, it doesn't degrade but only brings out the headphones true potential. In fact if you listen to Mp3's you end up clearly hearing all the side effects of compression.
But more importantly whatever qualities are lying dormant in your headphones potential is immediately brought out with class.
The other amps i auditioned were a joke compared to these. Go Vibe appears to know a thing or two about amping, they are simply superb. I only ever heard of amping recently because my HTC Phone was not giving me satisfactory volume when running my Sennheisers 449's and 439's and i thought "Damn" what a joke, Sennheiser is crap, until the guy at Jaben audio here in Melbourne Australia explained to me that the harder the headphone is to drive, the better its potential for higher sound quality, he told me that he has $600 headphones that are near impossible to drive, but when they are being amped correctly, well hey.
Anyway he said that with higher impedance headphones the resistance in the copper coil is waiting for high power to drive it and bring out the proper attributes in the headphone, and thus i was fascinated, so i took in my HTC Phone and Sennheisers and had a listen, WOW! Now were talking, end of story, give me that amp. Yes Sir $78 please, What! I think to myself, then i haggled and walked away with the Go-Vibe Mini-Amp-Box for $50, i'm a happy camper, and you will not be disappointed if you get them, that's the truth. They are not ultra powerful, but they certainly send my Sennheisers to a much better loud level without distortion and that's all i was looking for. My advice, do not hesitate, i thoroughly recommend them, they solved my volume and clarity woes...Cheers!
PS: the 5 second wind up problem the former poster had is not prevalent in my case, he might have got a faulty one, or the makers of Go-Vibe might have since fixed the problem, i have had no such issue.