Pros: Good audio quality and isolation
Cons: Feels like it's tickling your brain
These are deep seated IEMs like all the others in Etymotic's range. Personally I would place them around the ER6i, and well under the ER4P in audio terms.
The only problem is that the tips, like all Ety's stuff for me, make my ears sore. It's bearable, but I can usually only listen to an album or two before I want to take them out. It's an acceptable payoff, but it means these are "sometimes" headphones that are exclusively for when I'm using the phone and where isolation isn't going to be dangerous; although that said, Ety have an app which feeds in background noise over a settable threshold.