I got the microphone version today, paid $40 on mp4nation, honestly, I've had almost no experience with IEMs past crappy earbuds, and I might be spoilt by headphones by now, but the M4s didn't impress me at all, I'm burning them in now but so far I'm a little disappointed, seperation is very sub-par, bass is just too much for my ears, none of the tips really fit me ears well, the smallest ones that you get are alright though and I get a nice seal, I must have small inner-ears. The M4s also hiss quite a lot, none of my other headphones hiss on the FiiO E11 but the M4 delivers an annoying low hum at all times, not a big issue when listening to music but quite annoying for quiet classical or between songs, the isolation is not bad.
I've had no complaints on public transport so far and they do dampen the outside noise a bit but nothing to write home about.
For $40 they're 'ok', I'd be fairly annoyed if I paid the $70 asking however, and I'll probably upgrade to the B2s as soon as I get chance.