Here's a short write up about comparison between the JH-5M and a few different custom IEMs.
These reviews are the product of listening through an iPhone 3G and HeadRoom Total Bithead amp.
I tested several songs on each IEM, both by themselves and with both plugged into the Total Bithead with one IEM in each.
JH-5M vs TripleFi 10: Listening to the TF10 and the JH5M makes the TF10 sound like a bass heavy monitor. The TF10 even sounds muddy, which is surprising as they're quite good themselves. The TF10's lack of midrange isn't something that's argued much-- the JH5M possessed a much wider soundstage, better clarity, and was more balanced than the Triplefi's. After listening to the JH-5M, it was almost painful to go back to the TripleFi 10's. By the way, I am using the TF10's with a set of Comply tips.
JH-5M vs UE 700: This was the most interesting of my tests. The UE 700's are the only IEM that compare well enough side by side with a UE 700 in my left ear and the JH-5M in my right. This test again brings about the awesomeness of the JH-5Ms. The UE 700 are a very balanced earbud with surprisingly good bass in such a small package. The treble is a little too much in the UE 700 though, and the JH-5M seem to have an almost perfect level of treble. Soundstage is similar, but overall the JH-5M sound better.
JH-5M vs Etymotic HF-2/HF-5: Another very interesting test, but the HF2 just aren't nearly as comfortable as the JH-5M. The HF2s are about as linear as the JH-5M in terms of frequency response, but they don't have the ability to punch as much bass-wise. The sub-bass of the JH-5M is incomparable. The JH-5M also has a wider soundstage.
JH-5M vs JH-16 Pro: As you all probably know, the JH-16 are very very very good. Still, there are a couple of songs where the JH-16 Pro just sound muddy due to the exorbitant amount of sub-bass. For example, the song London by Third Eye Blind, on the JH-16s the bass line almost overpowers the vocals. On the JH-5M, the vocals are more present but the bass line is still clearly heard. The JH-5M aren't as precise otherwise, but are very close. To me, the $650 price difference isn't worth it and if I were to recommend a set of custom IEM to someone, I would hands down suggest the JH-5M. For $500, the JH-5M are a ridiculous bargain. They have 98% of the capability of the JH-16 Pro with a much more reasonable cost. They are much easier to put in and take out and are comfortable for longer. I honestly LOVE both the JH-16 Pro and the JH-5M but I can't imagine using the JH-5M and ever thinking to myself "Damn... I wish I was using the JH-16s right now."