Pros: Balanced frequency response. Deep bass, airy soundstage, easy to drive, high quality materials, built like a tank.
Cons: Headband needs adjusting for optimum comfort.
consider these headphones in the same class and price range as the HD 25 ii. The packaging, hard case, high quality 1/4" adaptor, 2x Kevlar covered Cables, and headphones are all top-notch and appear very durable befitting their mil-spec rating. I have ~50 hours on them and they are still sounding better with use. I'm guessing that they will pretty much peak within the next 25-50 hours. I'm really liking these so far as an office/portable set to have in my work backpack.
Not unexpectedly they have a forward sound signature that is smooth, lush, and full bodied while still maintaining its composure across increasing volume settings. They are very balanced across the frequency range with a slight emphasis on the mid-range and great bass extension. I would recommend the m-80 for those looking for solid bass. The bass is really, really good. The m-80 has a moderately-wide sound stage with good air between instruments. Resolution has improved a lot during burn-in.
The m-80 is very easy to drive. I was surprised at how much volume was coming un-amped through my iphone. I have an Audinst HUD-MX1 portable amp/DAC for my home office and the m-80 are easily driven with the volume set between 9-12. Of course they sound great through my Schiit Lyr. The m-80 doesn't seem to be very picky about what is driving them.
This is my first on-ear headphone and I'm adjusting to the fit. They need a little more time on my head for final fitting adjustments to find the optimum fit. I am hoping that with additional wear time the ear cups will mold to my ear. I can easily wear them for 2+ hours at this point. I have a small-medium sized head so YMMV.
In the very beginning they didn't sound very special (no big surprise) so I just left them running unattended on Media Monkey for 25, now 50+ hours. Now that they are nearing more optimum SQ I will spend more time enjoying them. They are definitely keepers for me.