I mainly use these headphones for mixing and mastering (along with my Adam A5X monitors).
Comfort & Quality:
They are very comfortable to wear for long hours. The headband and the earpads are soft but still firm enough. The plastic used on the headphones looks and feels somewhat cheap, although I personally didn't have any issues with it so far. I've read comments online from people with broken headbands though. So, let's just say that I'd expect a higher quality feel on headphones that cost more than 300 euros.
Only (very minor) problem I've had with these headphones so far has been the cable connection on the headphone end getting loose. Maybe the connector wasn't properly in place to start with, cause this only happened to me two times in the first few days of use. I can't really comment more on the built quality / durability yet, since I've only owned them for a couple of months now.
Very happy with the monitoring experience. It's very easy to work for long hours with these headphones and the mixes translate very well. The soundstage is not so huge (compared to some AKG open-back models) but it is still there. I generally use them in combination with Sonarworks Reference, which gives them the boost they need in the low end (where they originally lack a bit of energy) and a minor correction in the high mid range, but really, the correction Sonarworks does on these is very minor, which shows that the headphones are quite flat to start with.
Oh and a very important note: I've read a million comments online about how it's super difficult to drive these headphones / one would need a powerful headphone amp and so on... Not really!! My Original RME Babyface (which is notorious for having not enough juice on the headphone output) can drive these headphones perfectly well, that is, to hearing-loss-inducing levels with great clarity.. but then again, loudness is very subjective, so you should try and see(hear) for yourselves.
All in all, I'd definitely recommend these headphones!!