Pros: Dirt cheap, Increases maximum volume and bass significantly, long battery life, small, light, strong slip, nice styling
Cons: minor at this price: low quality cables, not many in this price range and size
Got for using with my I9000GT and ATH-M50. I found that sometimes I wanted more bass and a slightly higher volume with some songs. The Fiio E5 solved this problem, for next to no money, hardly any extra weight or bulkiness either.