I recently bought one and it sounds really amazing! It drives my HD650 quite easily.
I have 2 concerns though. I would like to know if you guys have the same experience:
1- I couldn't find a way to keep the dongle constantly on. What's happening to me is that quite often when in between tracks the dongle shutdowns for a fraction of a second (red light), then when comes the next track in the playlist the dongle automatically turns on again, doing this fade in so that I lose the beginning of the song (around 1 second).
2- I couldn't find a way to turn off this annoying fade in.