Pros: Versatile, Small Size, Acceptable Performance
Cons: Amplifier is not powerful enough, Poor design, DAC sound is treble accentuated
I owned the Nuforce HDP for two months, I tried it with several headphones ranging from the 600 Ohms DT880 to the 300 Ohms Senn HD600 and HD650 and 62 Ohms AKG K702. Actually I wasn't impressed that much. I didn't feel that the amp had enough juice to drive any of the headphones mentioned above, and the DAC had too much emphasis on treble which seemed too exaggerated and unnatural to my ears. When listening to several audio tracks and in comparison to Headroom's Ultra Micro DAC I heard distortions in the upper highs that never showed in the Ultra Micro. The imaging and accuracy of the UM DAC was far beyond the reach of the HDP, but on the other side, the HDP performed better than my Marantz CD5004 regarding clarity and detail. The best sound I got from the HDP was from the Marantz CD player connected by coaxial/ optical connection. But USB connection sound quality was thin, harsh and lean.
The volume knob is made of cheap plastic and sometimes I heard static when moving the knob between 1 o'clock and 3 o'clock. On the other side, the HDP is very small size, very portable and it has many connections on the back which makes a great versatile unit for many purposes.
So all in all it is not a giant killer. It doesn't function as good as DACs or Amps double or triple the price, but you get what you pay for. A $200 DAC and a $200 Amp no more, no less.