Pros: CHEAP! Clarity.
Cons: Build quality. Thin cables
There's so much said about these.
I was positively enamoured with my Etymotic ER4Ps. I still am.
But I picked up a pair of RE0s cheapish. And sold my ER4Ps because these were half the price and almost as good.
The RE0s are smooth, clear, fast.
The only knocks against them are:
1) the fit of the different tips. They aren't as good in isolating sound as the tri-flange on the Etys. Also, I haven't found a perfect fit with any of them. And some are a real pain to put on.
2) The cable is really thin and feels fragile. I can imagine they wouldn't last if they got caught on something and yanked.
Otherwise, price-perfomance ratio puts these way ahead of single-driver designed IEMs.