New FS owner since yesterday. And a happy one at that!
My current set up is an Asus netbook streaming Spotify (premium at the moment) or playing wav/FLAC/MP3 320K through Foobar/Asio combo. Phones are HD 558 slightly modded using Dynamat. Previously I used a cheap external USB sound card and Fiio E11 amp.
My 'reference' set up is 2 way tower speakers fed by Audiolab 8200CD / Hedo preamp-amp / using XLRs / mogami speaker cables and furutech power cables, all set up in a proper sound system rack.
Starting with the aesthetics and the cutting edges debate, it is a very small and light gadget indeed. The frame has edges that can scratch furniture finish, if moved around carelessly. On the other hand, at least for me, the edges are not so sharp as to injure someone who doesn't push really hard against them. The volume knob is not easily manageable, trying to handle it from the sides. It is more easily used in a push-down-to-turn fashion. I am sure that there are many DIY ways to make the knob more user friendly. Up to 3-4 hours of use the Fulla doesn't get more than pleasantly warm.
Coming to the sound. It is the first DAC/Amp I use, so no real reference vs other similar gadgets (e.g. Dragonfly etc.). E11 is an amp only and Audiolab8200CD acts as only a DAC when used with phones. FS really elevated the music from the netbook for both ways (streaming and Foobar). E11 and the cheap ext sound card just made the sound bareable in comparison with the FS.
What do I mean by elevated the music? Dimensionality, tight bass, instrument seperation, organic feel, transparency, better dynamics. Not such a big sound stage difference, but overall music sounding alive. In short everything I enjoy from my high end set up (scaling taken into account of course). No noticeable static hiss upon higher sound levels and the HD558s are easily driven without resulting to more than 30% of the sound level used.
So overall for me FS has really made a positive difference! PSB M4U1s are on the way, so I am looking forward to listening to this pairing. I will also use a powered USB hub to minimize (perhaps) any notebook USB port static.
PS. Some of the tracks I use for set up comparison purposes are: This little light of mine (Chesky headphones demonstration disk), Angel of Harlem - The Pursuaders, If I could sing your blues - Sara K, The chain - Fleetwood Mac, Beethoven's 5th - Kleiber, Love lockdown - Kanye West.