Summary: I have tried the device several times, from a MacBook Pro and from a Windows desktop computer. I've tested it with AAC and MP3 files and with CD's. I "think" I can hear a difference at times, but it is hard to put my finger on it. I will say that it feels more pleasant to listen using the Dragonfly.
Pros: Overall I would say that I "think" the Dragonfly adds fidelity, cleanness, and listening comfort.
Cons: I'm still having trouble saying that I can hear a "definite" difference with the Dragonfly. The improvement seems pretty subtle.
Summary: I plug the DragonFly directly into my laptop, and I have a pair of entry level audiophile headphones that I use with it. They don't require a lot of power, so I'm not sure about using an amp. I use JRiver MC for playback. I'm satisfied.
Summary: I'd become interested in DACs and their impact on the music after buying some new components and doing some listening tests. The best overall description of what a good DAC can do is to add "presence" to the music.
Pros: Sound, Size and Price
Cons: I haven't done a comprehensive comparison of similar USB plug-in DACs.
Summary: This is a great little device that I'm using to drive a set of noise-canceling headphones. I'm hearing aspects of the music I've never heard before. I've been using it with both Windows 8.1 and a Windows RT tablet. Love it!
Pros: Lightweight, easy to handle, no drivers needed, and the LED tells you what level of fidelity your playback is at.
Summary: This little device exceeded my expectations, but there is a trick if you are running Linux Ubuntu 14.04. Using the little Dragonfly, all sounds are inaudible if the Sound Settings volume is below 100%.