When I connected the AudioQuest DragonFly to my computers I was pleasantly surprised that it interfaced perfectly with no configuration effort. Since the DragonFly is exactly like a typical USB thumb drive, excepting the 3.5 mm jack on the end where headphones and other output devices are connected, the only cable issues occur when you connect something other than a headphone such as powered speakers or a power amp to drive non-powered speakers. In such a case I would recommend a very high quality cable to maintain the full benefit of the DragonFly's sound processing properties.
There is no physical volume control on the DragonFly, no doubt because it's just a small USB device the same size as a typical USB thumb drive. Since you'll need the computer's volume controls with the DragonFly, how they work on the different computers can be a minor challenge. On PC's using Foobar2000, I keep the Foobar volume slider all the way up and open the computer's volume window after Foobar is loaded. I suppose you could set the computer volume to maximum and then use the Foobar slider, but in my case the Foobar volume slider is so small I use the computer slider instead and that works fine. There may be cases where one method is better than the other sonically, but I didn't find that to be significant in my case. On the Apple Mac I use iTunes only with WAV-format files, and there I set the computer volume to maximum and used iTunes' volume slider instead.
One thing I really like about the DragonFly besides the convenience of having a DAC and headphone amp in one little plug-in device is the fact that it doesn't get very warm in use. My air conditioner died about 36 hours ago and I've been running a laptop PC with the DragonFly in an indoor temperature ranging from 86 to 89 degrees F. While the DragonFly feels slightly warm after playing music for a couple of hours, it's surprisingly cool given the ambient temperature plus the fact that all of those electronics and the LED status light are contained in such a small package. The body is 1.75 inches long less the metal USB connector, the width is nearly 0.75 inches, and the height approximately 0.5 inches including the small hump on top which accomodates the 3.5 mm headphone jack. Fortunately the DragonFly includes a good secure cap for the USB connector, but I don't see a way to attach a lanyard to it.
For those people who have been using the headphone jack on their desktop or laptop computers, and assuming that those computers have USB ports, they should expect better sound using the DragonFly instead of the computer's headphone jack. The actual improvement with my computers is a cleaner sound with a greater sense of "space" and "air" around the instruments. The fact that the DragonFly includes both a DAC and headphone amp in such a tiny package suggests to most audiophiles that the DragonFly's sound would be of much less quality than the typical separate DAC's and headphone amps selling for twice as much or more. I don't own the more expensive separates myself, but I have other DAC-plus-headphone-amp devices such as the HRT Headstreamer and Audioengine D1, and I have the HRT iStreamer DAC-only for Apple i-devices that I use with the Objective2 headphone amp.
I don't hear anything to suggest that the DragonFly is less than a good upgrade to the computer's headphone output in spite of the very small size. Doing lengthy comparisons yesterday and today with the DragonFly and my other DAC-plus-headphone-amps, playing a variety of 96 khz music tracks downloaded from the HDTracks and DownloadsNow sites, I don't hear a significant difference between them. I did expect to hear some differences in the ultra-high-frequency harmonics and so on, but in spite of the amazing detail in these tracks and the resolution of the USB DAC/amp devices, there's so little difference that I could easily guess wrong about which is better than the other. I could tell rather easily that these 3 DAC/amps were better than the iStreamer plus Objective2 headphone amp (and I think the limiting factor there is the iStreamer) and better also than the FiiO E17 DAC/amp which has additional features.
I'm going to take a guess here that since the DragonFly costs about $80 USD more than the Audioengine D1 and $110 more than the Headstreamer, and given the very small differences in sound (for the intended users at least), I expect people will buy the DragonFly because of the small size and convenience of not having to use a USB cable, or possibly other reasons. If such a small USB DAC were used with audio systems driving speakers, then one extra little cable would probably not make any difference, especially since the cable carries only digital data and the signal processing and jitter reduction occur after the cable in the DAC. But used with headphones, plugging the DragonFly directly into the USB port without a cable is a great convenience, especially when a laptop computer is being used away from the home desk/workstation.
An important issue to consider when purchasing audio components to improve sound quality is detail, i.e. how much additional detail will be revealed in the music tracks by the new components. It's possible that a new audio component could reveal existing distortions in the recording in a way that makes them less pleasant to listen to, and some buyers may experience that dreaded feeling of "Uh-oh, I need to buy more stuff", or "Crap - this isn't working out the way I expected". I didn't have that issue with the DragonFly though - the sound was more revealing but less harsh, which is interesting since I would normally expect more harshness and sibilance with the greater detail. I suppose it's the natural result of having better components to process the data in those digital music tracks.
Questions have come up in several places as to whether a typical computer's USB port can supply enough power to run the DragonFly's DAC and headphone amp, to provide good volume especially in the bass where the greatest power demands occur, and to have enough headroom to avoid clipping or otherwise distorting the loudest most dynamic music passages. The answer seems to be yes, since I have many FLAC format music tracks with a 96 khz data rate that have extreme dynamics which distort noticeably when sufficient power is not available. Some of those tracks that I've made 320k MP3 copies of for playing on the iPhone will not play on the iPhone at the full volume I prefer because of the extreme dynamics, however those same MP3's will play without clipping on the computer using the DragonFly DAC and headphone amp. Headphones tested with include the Shure 1840, Philips L1, ATH M50, and B&W P3/P5.