Pros: Open-air, 50mm drivers offer impressive extension, comfortable, light.
Cons: Unweildly cable, too large for some, glasses-wearers need-not apply, bassheads need-not apply, not collapsible.
Firstly let's get some things squared away:
I do not believe in break-in. (Burn-in for those who don't understand terminology.)
I do not believe cable materials alter sound.
I do not believe amping makes a large difference.
Ah, the sub-$100 market. SO much competition. I've been a self-proclaimed audiophile since late 2010. I started out with Bose Triport, and SoundMAGIC PL11. Since then, I've explored the $20-200 market very thoroughly, mostly staying in the sub-$100 market. Of this, I have had the pleasure of owning:
Audio Technica M50 (purchased for 60. I firmly believe the T500, which retails at $80, is superior to M50 sonically.)
Audio Technica T300
Audio Technica T400
Audio Technica T500
Audio Technica ESW
I've also had the opportunity to demo, at-length, just about every other mainstream $100~ range headphone. (Mainstream by Head-Fi's standards; Shure, Ultrasone, Beyer, AKG, KRK, etc.) I've been doing extensive comparisons, and I believe that these might be the best all-round ~$100 cans currently available on the market. Can be purchased online for about $60-$70.
Sonically, let's observe:
Bass: Reaches down to 10hz. It extends very well in to the sub-bass. Plenty of rumble, but not a whole lot of punch unless it's called for. For lovers of Djent, you'll adore the texture of Animals As Leaders's, and Ever Forthright's kickdrum, as well as fans of more ballsy power metal such as Secret Sphere, Vision Divine, Vulvagun, etc. It does darkstep, and more commercial dubstep impressively well for an open-air can. BTW, don't let the apperance fool you, despite the back being opaque, it's a metal mesh, and to my ears, is very nearly as open as Grado cans.
Mids: This is where the Pioneers really shine. Presentation, and tonality are incredible. Guitars really sing, and grunt when called for. Bass guitar is ridiculously clear. Steve Harrison shines exceptionally. Mids are also laid on thick when necessary. Lovers of Sludge, Drone, Crust, etc: This is handled incredibly well. Fall of Efrafa, Downfall of Gaia, Celeste, and Converge sound excellent. Agalloch, Black Sabbath, and Insomnium as well sound amazing. It's weird how these cans do it all. When called for, they convey the darkness that these genres call for, yet due to the open-air, and massive 50mm drivers, as well as the gigantic driver baffle and velour pads, its extremely spaceous, and airy. Nothing gets muddied. VERY fast cans. Chaotic Hardcore, Noisecore, Grindcore, etc sound great.
Highs: Sparkly. There's not much to say. It's very reminiscent of Grado, but airier. I haven't heard ATH-AD500, ATH-AD700, or ATH-TAD400, so I can't compare. It never gets sibilant, unless the track is mixed to be sibilant. It can get a little hot with super bright tracks, but just drop the higher end slightly on the EQ, or lower the volume. These are in-door cans, so if they run hot, I personally recommend just to drop the volume rather than affect overall SQ with EQing.
Live Music: ...These are the best cans I've ever heard for live recordings, even up in to the $200 range. ATH-A900X, Dennon AH600, D2000, Sennheiser HD600, Ultrasone PRO580, Shure940, Grado SR125/225 can't touch these when it comes to Live presentation. (Sorry if I get any model numbers wrong. :P) Their stereo positioning is impeccable. The stomp and cheer of the crowd, the sound of acoustic drums, live vocals, everything shines through. You can really feel, and percieve the sense of the large stage. Especially in open-air concerts, like Iron Maiden's "A Real Live One", or the sense of being in a concert hall, like with Joe Satriani's music hall performances, Yuki Kajiura's performances, live baroque recordings, or the sound of being at "The Assembly" with Machinae Supremacy.
Mostly metal, with a solid plastic double headband. It's self-adjusting, much like the ART Monitor series of ATH products. Huge, plush Velour pads. Behind the pads, is a massive piece of felt over the front, covering the driver and baffle to filter out HF. I haven't experimented with removing it, but I would assume it would make the HF white hot. The cable is thick, and protected by a thick woven cloth sheath. Strain relief is very solid, and positioned well. The jack is an extremely thick gold-plated 1/8th jack. The strain relief is kind of like a slinky. It's flexible metal. The TRS jack itself is gold, whilst the housing is solid aluminum. It's threaded, which works well for threaded 1/4th TRS adapters. For the DIY-minded purchasers: I recommend unsoldering the stock cable, and wiring a second gold-plated i-plug on the back for studio use. This cord is very well-made and worth salvaging for home/studio use. I also recommend cracking it open as it is single-entry, and sticking a 1/8th female pannel-mount within the cup, and buying V-Moda's audio-only cable. This will greatly improve its transportability.