For those looking for comparison against the Xiaomi Pistons, keep in mind they are open back IEMs (they don't isolate that well) to some extend is not fair to make a decent comparison. The whole purpose of IEMs is to isolate a bit from the noisy environment IMO and if you don't really need isolation I don't see why would anybody prefer IEMs against full size headphones. The hard part of designing headphones are precisely making a good sound out of so many reflective surfaces in a tiny closed enclosure.
As far as I know I've never seen or heard an open backed IEMs before. The vent or vents on IEMs are there for a purpose as in bass response but the little tiny vent will make very little if not any difference at all in sound isolation.
Edited by Francisk - 7/2/14 at 8:58pm