Pros: Very versatile; genres and file types. Slamming bass, sweet mids and beautiful highs without the "daggers in ear" effect.
Cons: I didn't order a Wizard design.
These are my first CIEMS, and I took quite a blind plunge as I brought these when there were about 2 reviews. I've had them for just over 2 months, and my enthusiasm for them is as high as when I first got them.
The other reviews are more in-depth/useful; I can only really echo what has been written about them.
For me, the most notable things are that the bass slams very hard when needs be. The highs are extremely good, without any hint of piercing, that my old IEMS had. For me, this alone goes a long way to justify the price. I've never really understood soundstage before, so that will have to be covered by other reviews.
The comfort and fit are everything I need. No longer do the units shift/ fall out of my ears when I'm walking.
About the only thing I regret is not buying a Wizard Design. And this is even though I didn't buy it in the Black Friday sale, which is testament to the K10's quality.