I bought this for fun (it's so damn cheap).
Running: iPod Nano (latest Gen)-> Fiio E1-> Magnum Alessandro MS2i.
While I seriously wasn't expecting much, I was quite surprised. It drove the Magnums really well (punchy, good bass control). Soundstage is a little compressed compared with better amps. BUT...
For $15, I really can't complain. Plus it's so compact. I ditched the E5 I have.
While my RSA Predator is my portable amp of choice, the Fiio E1 will get a run simply because it's a simple, elegant solution (GENIUS actually) that combines: amp, LOD, music control/volume control in ONE device.
For the revisions, I'd like:
1) a slightly shorter cable
2) a HOLD button!
Gonna try it with my Ety Er4P and 4S now...