Had the HP50 for years as my daily driver portable starting in 2014. LOVED the sound without EQ, but after 3 years, one of the drivers started to play at a much lower volume (regardless of which entry port is used). They replaced it with a refurb at no cost, which was awesome customer service. Unfortunately the refurb developed the same issue after 6 months, and since they were still near MSRP of $250 at the time, I wasn't going to get another pair to have them failed.
Tried the HP70 (which are a wireless headphone) as a replacement, but I hated the background hiss when using the "Room Feel" active wired mode or wireless mode. Passive mode sounded absolutely terrible. I get why they'd include an active mode with corrective EQ, but I have no idea why they didn't use the same acoustic tuning as the HP50 for passive use.
So because of that, I got the Sennheiser HD1 wired version, which I didn't like quite as much, but they did the job for portable use, and they were a LOT more comfortable than the HP50. Now I use the Drop Panda as my portables, and I love them. Sound is somewhat reminiscent of the HP50.
BTW re the headband discussion: Both the refurb HP50 and original had the flat headband, unlike the curved I'm seeing in recent images. I got a lot of negative comments about the looks of the headphone due to the headband, but it was comfortable, and easily got a seal on the earcups. I think the round headband will have a harder time sealing the earpads. At least that was the case on the HP70, which did have a round headband.