My biggest qualm with the Etymotic IEM's is
their THD metrics granted these are the ER4XR, I would safely assume the THD is identical after the bass frequencies.
Comparing them to the Sennheiser IE 40's it's a pretty significant difference, especially for the price ($99 vs ~$250 to $300+). The thing about the IE 40's though is the crux of many IEM's these days, that being treble is slightly elevated (well not slightly, more like 15db at the apex of the spike at 10,500Hz).
The seal of the Etymotic though is obviously legendary, and is a massive selling point if you ask me for people who commute the way I do here in New York City.