Pros: Phenomenal sound, compact, and lightweight.
First off, I just got off a 14 hour shift and I'm a little too tired to be very descriptive and detailed, but I'll do my best :). I have a pair of M-80's and I never was able to fall in love with them. That being said, the XS is the "new and improved" version of the M-80. There are a few key changes with the XS. The clamping force is significantly less and much more comfortable (while still staying firmly on your head). The sound is slightly different but quite amazing. One of the things I didn't like about the M-80 was that headphones produced a higher treble that I prefer. From the moment I first put the XS on, I loved them. The sound was crisp and firm while being very balanced (keep in mind, this was just sound quality from an iPod with no amp or eq settings). Once I used my iPod paired with the Vamp Verza, I was overwhelmed with such amazing sound (in a good way). Both times I listened through the XS, it was within the first couple hours of being used, so they weren't even close to being burned in. Now that they have been burned in, the sound isn't as crisp, but it blends in much better (I can still tell the individual instruments clearly when listening to classical though). They are small and exceptionally compact. When I first saw the case, I thought the headphones would be much smaller than the M-80's or any on-ear headphone in general. But sure enough, I unfolded them and loved them before testing them out. One of the great things I also like, is that they are extremely light. They weigh about 60% of what my Nokia Lumia weighs. I am a massive car enthusiast, so naturally I had to test these beauties while watching Ryan Tuerck Drifts the Wild. It's crazy just how much you can tell when listening through these. Turbo spooling, tires spinning, grabbing the ebrake, and even the leaves moving as he drifts past them. The quality is just outstanding (I really don't think I can emphasize this enough, haha). I can't go into all the technical details like some people, but what I can say is that I love these headphones. It's hard to find compact, extremely lightweight, comfortable, and quality all in the same package. To add a note, if you have the M-100's and love them, you'll definitely love the XS's.