I got one about a week ago to use with my RE0 IEMs, which required me to have the volume on my iPod classic at ~80% for normal listening.
It really brings out the depth of good headphones, and I have noticed my iPod even lasts longer.
However, the clip is poorly designed. If you want to attach it, make sure the iPod is either off or the cable is disconnected because you WILL press buttons when trying to attach.
Also, the cable is unnecessarily long, and makes me have a lot of extra wire.
But in the end, I really think its worth the ~$20 I spent. I bought it over the E5 because I really didn't want something else to charge.