-JH16 was my perfect CIEM or headphone I ever tried. However, for a nice late night listening session they were a bit too relentless. The detail and every frequency on steroids was awesome for general listening, but when you wanted to kind of unwind, really not the greatest imho, SS very wide, but depth isn't the greatest
-Merlin was enjoyable, but didn't have the top end sparkle I was looking for, poor isolation due to venting, I like to be isolated more from the environment I found..
-Miracle awesome mids and realism, but less bass quantity than my TF10
-TS842, great hybrid CIEM, but at the time I wanted more, slight edge to upper mids and treble, clear upgrade to TF10
Oddly enough of those customs, I've kept my UE Triple Fi 10 custom, it sounds great, I can take it outside of the house without worrying too much, and even work out with it.
I think everyone has covered the negatives pretty well here are mine:
-Initial Cost-including impressions
-you take a huge hit if you resell
-if you want to try another custom you go through the entire process again PITA
-I actually had impressions made about 3 years ago and due to them shrinking a bit or my ear canal changing, if I wanted new customs I'd have to get the impressions again
-Taking a $500-$1000 custom outside of the house made me paranoid that something would happen to it, so they mostly stayed in the house.