So I just got the NAD HP50's and my thoughts so far as it pertains to what I have used so far (Harmon Kardon CL, HD25-1 II, Momentum On-Ears, Bose IE2, Etymotics HF5) in my continued search for comfortable portable noise isolating headphones:
1) The cables are really short. Even from my close position to my work laptop to my headphones I am constantly accidentally yanking on the cables. Fortunately I am getting an extension cable to solve this issue but compared to my HD25-1's generous cable length it is sort of annoying I have to resort to that for an extra foot or two.
2) The isolation is about the same or slightly worse then the HD25-1's which is a shame I was really hoping the Over-Ear form factor of these headphones would isolate better. I feel like with slightly more head clamp this would be a lot better in my completely unscientific study of applying slight pressure to the ear cups while listening to music. Which also boosted the bass's boominess I found.
3) I do find them comfortable. It took me a bit to figure out the proper headband placement (Which is really a weird and awkward design choice) to not find it noticeably annoying. But I my ears apparently fit quite comfortably and no pressure against the ear pad that I notice though it does touch it slightly but not enough to be annoying. My HD25-1's start to get annoying after a few hours something I have not had happen with these yet.
4) Sound-wise I think it really comes down to what sort of music you listen to. I really like my classical music and movie soundtracks. On the HP50 I do feel classical sounds much more defined. The brass and horns sound just right and in your face like its supposed to without the bass overwhelming the overall sound. But when I get to movie soundtracks some songs really are much about the bass and I find those songs sound better on my HD25-1's. For the few things I listen to with vocals I find it does sound a lot better on my HD50's then the HD25-1's.
Overall these are just my general opinions and are no way of that of the more skilled people on this forum who have much better hearing then me. But I wanted to post what I found in case some people had the same questions.
I really like them. And they are portable for me about or slightly more portable then my HD25-1's since this can fold in they fit in my tiny bag slightly better then the HD25-1's do.