I've had the JH13 for a little over a month and couldn't be happier with them. Some qualities that have continually impressed me:
Transparency - The JH13 do lean slightly to the warm side of neutral.. but they're more transparent of recording quality than any IEM (custom or otherwise) I've heard. While they don't ruthlessly serve up the unsavory aspects of poorly recorded material.. they do let you, very clearly, hear the lack of dynamics, imbalanced tonal qualities, and poor soundstage of poorly mastered audio. They're a lot like the T50RP Paradox in this respect: very revealing, but not grating or clinical in presentation.
Cohesion - I've completely forgotten this is a multi-driver, BA-based IEM. All six drivers (and the crossovers) work in a remarkably harmonious, unified manner. The smooth nature of this phone isn't simply due to tuning, there's clearly more work that's been done here to maintain such an effortless, natural presentation. It feels a lot like the HD800 in this respect. A little difficult for me to describe, but the JH13 sounds very much like a very advanced dynamic driver.. that isn't plagued by the problems that (typically) affect many dynamic drivers (lack of speed, clarity, distortion, etc.)
Soundstage - As I've spent more and more time with the JH13.. I've come to become stunned with the soundstage and imaging (particularly when the IEM is driven with dedicated upstream gear). Again, it's better in this regard than any IEM I've owned... UM Miracle included. It's incredibly precise, open, and well proportioned. As a listener, I feel situated at the proper depth from the stage/performance.
Resolution - Simply put, this phone is capable of resolving at HD800-levels, IMO. Tonal reproduction is very natural, articulate.. and clearly TOTL.. it's ability to retrieve inner detail is phenomenal. Unlike anything I've heard from another IEM. It's resolving ability.. combined with the smooth signature, soundstaging, and driver cohesion make for a listening experience that feels extremely natural and realistic. Obviously, dedicate upstream gear is required to squeeze out all the JH13 is capable of.. but I've been more than happy (and extremely impressed) using the JH13 with "just" my Galaxy S3.
It's difficult to quantifiably justify the (high) cost of the JH13, but after having had time to use it (daily, for at least three hours.. for the past month plus), I feel the money I spent on it is justified by the amount of pleasure (and value) I'm getting from it. It's the last custom I envision buying for the foreseeable future.. and I find it extremely difficult to find any glaring faults with it... even in the face of a well-driven HD800, IMO. I still plan to buy a universal IEM or two from time to time (i.e. I'm excited about VSonic's upcoming offerings).. but as far as customs go, it's going to take something extremely special to coax me to make another trip to the audiologist.
If you hear something a bit off, you need to look elsewhere in the chain. They're generally better that what you use them with without being too critical of poor sources. Their very even response and slightly added weight keeps them listenable. Detailed without being bright.