Just created an account here to give an average (i.e. power these specifically with a mobile device only) impression on these headphones. Please remember opinions are subjective and I'm in no means an expert on sound. With that said, I picked these up in Yodobashi Camera in Yokohama two days ago and it took me forever to find them. I had to look in the new headphone guide they put out to find the M-100s and asked a store representative to help me find them. A couple minutes of my mediocre Japanese later, I left with a pair of M-100s in Shadow for 27800 Yen and an AT-HPH300 headphone shelf hang mount thing. Totally off topic, but I so wish we had stores like this in America. There was a whole isle of what seemed like ~300 headphones hanging there with tags (Imagine how Toys "R" Us did video games a long time ago) to bring to the cashier. Not only were the headphones out for display, they had jacks to test them out with your own music. That, paired with the awesome customer service make me love Japan. Okay, onto the real part
Design: Aggressive, and when I was riding the train a lot of people would stare. The satisfying clicks when you fold 'em up are great and make you feel like you got a quality product. I also took the headband and started bending it in a bunch of contorted angles and they feel quality. When you hold 'em, you know you got a quality product.
Sound (Driven right out of a Motorola RAZR M)
Bass: Quite a lovely kick, and I love it, but I think it's because of where I grew up (Bay Area, California) that I adore bass that gets beat into your ears. It's not just the kick, but it's quality as well. No distortion what so ever and it leaves a nice, subtle rumble on your head depending on what song you're listening to.
Mids: I wouldn't say the bass is over powering, but the mids are like, I dunno, a smidgen? below the bass hits. They sound warm and detailed when you got some acoustic songs, but with mixed instrumentation you're going to hear the bass more
Treble : Same as the mids, they sound great on an acoustic arrangement but also are a smidgen below the bass. Don't get me wrong, they sound great, but like I said before, they are just a tad bit below the bass.
Closing: IMO, the best portable headphone to be driven solely out of a mobile device. They attract a lot of people and bring out the small details. Sometimes, I do wish the highs came out a little more but tuning the EQ to that specific song fixes most of it. Overall, I think it's worth the money. Remember, opinions are subjective and these are only from an average listener like me.
P.S. The napkins in the ear cup make the sound stage a little bit broader and , to me, sound better. They are also a little more comfortable