Holy crap, $80?? I thought I stole my M500's at $149.00 (regular price $299.99),but that's a killer price.
I like mine but they are limited in how/where they can be used. Very low "clamping" force makes them extremely comfortable, though the down side is you can't be active when using them. My impressions are that the on-ear pads are far more comfy for me than common over-ear cups. I don't get sweaty ears at all, and can listen for hours. They sound remarkably like my R500's, though of course the sound is imaging in a completely different way.
That deal on the M100's was too good. I succumbed and bought two pairs.