Yes. I've tried the Momentum many times but never was really impressed with their sound; and I'm a huge Sennheiser fan (I've owned the 558, I like the Amperior, have HD650 & HD7DJ currently). The sound coming from the NAD's surprised me SO much, I had never been so impressed with a headphone on the first try. I always kind of depressed when switching from open cans to closed, but now with the NAD I don't mind when I put them on my head. Comfort is hit or miss, you really have to try them for 2 weeks. I got used to the headband after a week.
This is just my opinion so take it with a grain of salt. Read a lot of reviews of both and see which suits you best:
- Very dark treble
- More bass than NAD
- Much better headband
- Outstanding build quality
- Smaller sound stage
- More portable
- Awesome Sennheiser warranty and customer service
- Much cheaper
- You can get refurbished pairs with a full 2 year warranty can be had for $199 sometimes $179.
- Small earcups
- Open, balanced sound with non harsh highs
- Headband may not be comfortable or may take time to get used to
- Earcups are small for some, not for me though
- Instrument separation is really good
- Basically a closed version of the HD650 with the highs not as soft, but the highs are not harsh on the NAD
- They feel very fragile so I wouldn't really take them outside the house too much (but my PortaPros also feel that way and have survived through everything)
- It seems like they really sacrificed build quality for the sound
- Refurbished pairs can be had for $210 but with only 1 year warranty
The best review I've read that describes the HP50's is http://www.technoheadphone.com/headphones_earphones/nad-viso-hp50-review-king-300-headphone/
My honest opinion:
If you want a closed, more portable headphone, with style, with good sound for cheaper, get the Momentum.
If you want a closed can that does all genres well, sounds very open, is balanced, but isn't really as portable, get the HP50.
Anyone who disagrees please post your opinions!
Hope this helped.