This is my first portable headphone amplifier, so I have nothing to compare to.
I can however compare it to the sound I was getting through my Cowon S9. Although the Cowon produces a fantastic sound, put this little beauty in-line and the headphones come to life!
I am using it with the Hifiman RE-ZERO's and I have to say it is the best audio experience I have ever had. The E6 has 3 EQ settings, all of which make a noticable difference to the sound. If one is a bit flat sounding for your liking, flick the switch and hear the bass rumble.
This will make your earphones go louder, if that's what you're looking for, but also it will make the sound more rounded. Deeper bass, even sub-bass. Clearer mids and more extended highs.
At this price it is an absolute steal. If you are in the market for a small, ultra portable amp then look no further. It even comes with a spare clip, just in case you manage to break the very solid first one.