Most UE18Pro owners here seem to be quite reluctant to talk about them, but if you are looking for neutrality, UE18 are definitely not for you. Here's a comment I made in another thread:
My only experience with custom IEMs are the UE 18 Pros. In terms of looks and built, I don't think they can be faulted and mine fit my ears perfectly first time round. However, sonically, I really don't think they deserve the $1,350 price tag, I'd rate my Westone 4, UM3x or Turbine Copper higher. There seem to be a big bump somewhere in the high frequencies, and for the last year or so I've been wondering if maybe they were faulty or there's something wrong with my ears that made them sound that way. Then recently I found some frequency graphs of the UE 18 which confirmed my doubts.
If these graphs are right, there is a big bump around 7-8 k which takes out all the sparks in music and gives a very dull sound in general, kind of like the opposite of the HD 800. I've often wondered if that was done deliberately to minimize ear fatigue for stage performers which they were primary designed for, and if that's true, maybe they should warn potential customers about that before they made the purchase.
Although I've not heard the JH 16, just from looking at the graph above, seems to me they have that similar 6-7 k spike like the HD800, do they sound bright and sibilant?
After my experience with UE 18, think I'd give custom IEMs a miss from now on unless I start doing live performances. Right now I'm quite happy with my Westone 4 and UM3x, especially the W4, which to me is nearly as good as my LCD-2.