Pros: Neutral, balanced sound; excellent isolation; comfortable fit
The JH13 Pro was my first purchase of high-end personal audio equipment so it's difficult for me to provide a fair comparison (prior to purchasing them, I was listening to iPhone earbuds), but I can safely say that I couldn't possibly be happier with my purchase.
The process of getting the impressions made was painless (albeit a bit expensive in the San Francisco Bay Area), and about a week after I had the impressions made, my JH13s were waiting in the mailbox. The fit is excellent (as you would hope in a custom IEM), and the sound quality is tremendous.
My only real criticism is with the cable. I suppose I don't really take care of my monitors particularly well, but the cable is coming unraveled at the end with the jack connector, and it really annoys me. Also, I'm not thrilled about the look of the clear plastic molding--I purchased an Aerous VX3 aviation headset in black from Jerry Harvey at the same time and much happier with the look of the opaque headset than I am with the clear ... but that's my own fault.
If you can afford the steep price tag, you can't go wrong with the JH13 Pro (unless you want the extra bass response of the JH16).