4 or 5 stars

This is still the question of the many reviews.
I'd like to answer it briefly.
Only in combination with the E 12 amplifiers are 5 star for the sound reasonable! Me Little described weaknesses in the software and the service, but cheap ring made. The sound quality is ultimately crucial. The amplifier does not always bring more high-end, but by the very specific bass enhancement on current charts, more fun and pressure in the ear cups.
Currently, there are in this price range no sound alternative. This is crucial point. Astell & Kern AK 100 is the benchmark here!
My Headphones: Beyer T70P and B & W P3
Experience with Fiio E11 and various Apple MP3 devices.
Who the ease of use is just as important and disturbs somewhat chunky appearance of the two devices, here comes naturally to another vote.

After prolonged use, I would like to add my experience:

When Beyer T 70P quality is important without glasses! Sounds weird, but it's true! The amplifier E12 is always worthwhile !! The fine adjustment of the volume control via alone is already worth the thing.
Then there's the bass boost in not perfect (MP3) music!
When Duo E12 and Fx05 I forgive sounded technically 5 points that Preisklssenbezogen are!