The Momentums were one of the most...confusing headphones I have ever used. Too dependent on a fit and seal that was impossible to obtain, though I could get glimpses of decency after much fidgeting and often using my hands to position and seal the headphone. At that point, it's pretty much a worthless product for me. YMMV indeed.

Even during their better moments, they were still "meh." I'm not sure how these were so well received in many places, though product variation could be a factor.

I think these might share a very similar driver as that in the HD4x9 line. The driver and baffle looked the same or very similar. Measurements can be strikingly similar at times, though impedance measurements are noticeably different. The HD4x9 headphones might not be built as well or look as cool as the Momentums, but they at least fit and seal properly (you know, an actual over-ear headphone). The HD429 was a solid headphone and didn't do much wrong for $50 or so. I would not hesitate to take that over the Momentum based on my memory with them.