Pros: Clean, detailed sound, powerful and deep bass, wide soundstage, S-Logic Plus tech, very good looking
Cons: None so far.
I've bought these HFI-780 a while ago and I'm really happy with them! Spectacular, very refined sound and the bass is full and clean. I've decided to buy these professional high-class headphones after a deep research and following some pro musicians recommendations (had to choose from HFI-580 and HFI-780).
At first I was skeptical, but I really like S-Logic Plus technology. Despite what I've read on other reviews, they have very deep and powerful bass, but that may depend on the player they are connected to. Eg. on a Sony PSP or on a PC with quality sound card they are INCREDIBLE! The mids and highs are very accurate and detailed (these headphones are intended for Studio use). I have to mention that they have also a great sound isolation.
They are comfortable even worn for long periods (4-5 h), but generally that depends on size and shape of the head (mine is medium sized). The cable is kind of short but is thick and it's appropriate for all portable devices; also they came with a longer extension cable (about 4 m). Another thing I like about them is that they are foldable and both cans can rotate.
I find them a very good upgrade from M50 because they are definitely better; I think that these are among the best headphones (if not the best) on this price range and is definitely worth the money!