I previously owned the UM2 for more than 3 years and had a lot of fun with it until i gave it away last year. I heard a lot about the SM3 but i never expect it to be this good. The bass, detail and soundstage surpasses the UM2 in almost every way. The bass is as much or even more than the UM2 but much faster and more controlled, smooth mids and almost no hiss. The soundstage is huge and amazing. Seriously I´d take these over everything i currently own when it comes to music listening including my Razer Mako, K701 + Heed Canamp + V-Dac.
+ Controlled, punchy bass
+ Huge soundstage, make me feel like standing right on the dance floor
+ Sound great with all kind of music
+ easy to drive, sound great straight out of my Clip
- Looks and feels very fragile unlike the UM2
- Hate the edges around the earpiece
- The V-shaped cord might be too short for some