I've had the HP50 for about a month now and I'm loving it! I agree with most all of the sound-quality related praise it has received. A few notes:
- Yes, the headband design isn't the best, but the metal is flexible enough that with continued use and some intentional bending (like the flat bill of a new hat) the band gradually forms a curve that fits better across your head. After a month the headband is actually super comfy to me. Still doesn't look the sexiest, and I think it should be redesigned when (if) NAD's successor to the HP50 is being developed.
- Coming from a slightly pedestrian Sony closed-back with heavy bass, I initially felt the lows were a bit lacking on some songs on the HP50. Good on analog / bass guitar recordings, a bit weak on (certain) digital pop/EDM/hip-hop recordings. However, I picked up Audioquest's Dragonfly DAC/amp (1.2) and once it was set up properly, the bass was richer, the sound was "fuller" and it breathed life into some of my less-dynamic recordings.
- I prefer to use this headphone as a "portable" headphone rather than a "mobile" headphone. What I mean is that the HP50 is very easy to stow in the included case, along with the included accessory pouch (you can also put the Dragonfly or other small USB dac/amp in the pouch comfortably), and throw it in your computer bag or luggage. It doesn't take up much space, and all you need is a source (usually for me, my Macbook Air) for fantastic sound on-the-go. My job sometimes requires me to travel and spend a few days in a hotel, and a "portable" solution like this is awesome for me. Now, for "mobile" applications (listening while walking around, in an airplane, etc) I prefer IEMs, because I can comfortably fit them in my pocket, they look better, and I can do the "take one earbud out" trick when I have to be aware of my surroundings or talk to someone.
- I wish it came with a better/longer cord, or that more aftermarket options were available. Right now I'm looking at Alpha Design Labs (ADL) iHP-35 (http://www.adl-av.com/products/cables/headphone/), because somebody in another thread confirmed they work on the HP50. Wondering if it's worth the ~$100 or if I should just get one of the V-Moda cords for $20.
TL;DR VERSION: Headband looks dorky but comfy after break-in; HP50 + Dragonfly is an amazing cheap (~$450) combo; needs better cord.