Pros: Increased Volume, Increase Bass
Cons: Bass boost can sound bloated
For 20 bucks, it isn't a bad piece of kit. Nice little volume boost, added bass kick to my SRH440s. Really can't go wrong if you want something tiny, portable and have a bass light set of cans or IEMs.
The only con I really have with it, is that the volume down button is VERY close to the headphone out jack. If you have a set of phones that have a large plug the minus button can be hard to hit. Other then that it's a nice little starter portable amp. Now it lives in my car, to boost my phone going into my AUX in jack, which is very quiet.