Pros: sound, portability
Cons: leather pads are not suited for longtime listening, internal conections leading to slight channel imbalance
Im not used in review writing, but since I am so happy with these cans, I have to write something
I bought used M50S (six months old) for very good price and in really nice condition. I've decided so because of lot of traveling around the world. And these are solid and nicely portable.
Together with Mini3 (wall connected) and uDAC2 fed through ASIO with FLAC files the sound is quite decent. Stage is there, instruments are not as detailed or revealing as on RE0 - but only at first sight. In fact, I found lot more details in soundstage, instruments or sound sources are separated, also there is really nice slight echo in the stage when it should be there. After modding (OXOOOXO mod on lower holes), mid bass is more polite, better behaved, not that disturbing like out of the box but still very low. But this is a question of taste. Overall sound is good balanced, higher mids and highs are good recognizable, enjoyable and it sounds like they have something to offer, even they are not that mouth-opening like in RE0 at first sight, but they are still clear (wait man! these cans are closed! ).
Definitely worth the money!
EDIT: After few months with these on a head, I found it better to add an extra supply for the uDAC2 (f.e. through USB hub) than applying the mod on cans. Results in details and frequency response are incomparable.