I think it's very important to mention these are OPEN-back, which won't be suitable for everyone & not for outdoor use. Plus, as they're rated at 250ohms, they need something substantial (e.g. proper amp/dac) to drive them / get the best out of them. No wonder they have 500+ of them to get rid of: "Customer sent back, as it wasn't suitable for their needs after trying it. Product works fine and tested and in perfect working order."
The P9 sig will be better but considering the P9's cost £400+ more that's to be expected.
for £3 more you can get them brand new on Amazon https://www.amazon.co.uk/beyerdynamic-990-PRO-Studio-Headphones/dp/B0011UB9CQ?SubscriptionId=AKIAJJXYVSIAIB2WQVLQ&tag=pjuk-amazon.co.uk-21&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B0011UB9CQ&smid=A3P5ROKL5A1OLE
These are b stock, no mention anywhere in title or description.
I have these with 600ohm windings and my mobile can still drive them fine. I would recommend the 990s.