I received my K10s in mid December. Before that, I owned another pair of CIEMs (the Heir Audio 8.A) which I have since moved on from. The 8.A was John Moulton's original 8 driver design, with a relatively dark, bass-heavy signature.
 
When purchasing the K10s, I was slightly worried that I may give up some of the sound that I loved so dearly. Man, I just didn't know what I was missing out on. The K10 can do everything that the 8A could do, plus more. The highs are incredibly well-detailed and non-fatiguing, the mids are incredibly natural, and bass doesn't overpower, but is still booming when the current track commands it.
 
I've seen other reviews mention that the K10 has less bass quantity than the 8.A, but I have not found that to be the case. Sure, the sound signature is perhaps less dark overall, but far more natural, and the bass is not lacking in any way, shape, or form. I've yet to come across a recording where I've not been exceptionally pleased with the sound quality.
 
Versatility is the name of the game, the K10s will pleasantly reproduce any recording you throw at them. With that said, it is very much so advantageous to feed them with a high quality sound source. I tend to only listen to ALAC files, through an HRT Microstreamer fed through Amarra, or through my iPhone 5s whilst on the go. 
 
Fit and isolation is wonderful, as I had my impressions taken by Brannan from Noble Audio, free of charge. If you happen to be in Southern California, I would highly recommend having Brannan taking care of your impressions, as he knows to take impressions to Dr. Moulton's standards. I had some seal issues on my 8.A's, but my K10s fit wonderfully. 
 
I will also note that build quality is second to none. My K10s are absolutely flawless, and beautiful to boot. I opted for a Wizard design, which was 100% worth it, especially since John took care of me with a design that I have still not seen on an IEM from Noble or any other company.