I have no experience of them but I fail to see how something so small can offer anywhere near the experience of over or even on ear headphones. I've seen some that cost so much I wonder if they even sell any.
Ok, so think about it this way:
Balanced armatures (the most common drivers in IEMs) are like miniature planar drivers. They're very small and super efficient, so you don't need powerful amps to power them with authority and tight tight control. And then, the more expensive ones will have three or more (I've seen 12!) different BAs that are specially tuned to play a dedicated range of frequencies really well, so you might have one BA tuned to play highs, one for mids, and another BA (or Dynamic driver) play the lows. Sometimes different frequencies are separated to play through different tubes right up until they reach your ear canal.
The result of this is almost no bleeding-over effect, and stunning clarity and detail. Clarity helps your ear and brain distinguish between a sound that happened at a distance right in front of your face, and a sound that happened 20' away, slightly to the left. Imaging, the sense of a sound's direction, and separation, the sense of two different instruments not blending together into one, both are greatly enhanced by the clarity and resolution of a headphone.
If you get to hear one of the crazy, $1k+ IEMs, you'll realize they go toe-to-toe with summit-fi stuff like the HD800 or Stax SR-009. Do not underestimate the power of the inside earphones.
Hmm similar performance, all in one, alot cheaper then going for a modi Uber and magni setup, USB powered?
Unless I find something better for my needs (going to look up the E5 since I play handheld games as well) I'll probably go with the G5.
Yeah, the E5 sometimes goes on sale, slickdeals that ****!