I've been running some MEXT iems for a couple of weeks now, and I do have to say if you're a basshead and you want some IEMs, these are the most potent I've ever tried. I didn't know if they would be a bit of a gimmick, but man, they definitely have some bass. I also didn't know how well the bone conduction would perform with universal IEMs, but the bass is there, for sure.
The closest thing that I would have to contrast to them are OG Merlins. I also compared them to a pair Grado PS1000 headphones, and for the heck of it a pair of Sony WH-1000XM4 headphones. Those have 50mm and 40mm drivers respectively, and while Sony is known for bass, and Grado isn't, there is more bass from those PS1000 cans. Both have quite a bit less bass than the MEXT iems. Honestly, they are the closest thing to subwoofers that I have used on my head.
I listen to a lot of jazz, and I do love the sound of the bass (the instrument), and honestly, it's not just with hip hop, even with bass heavy jazz listening back to back, the MEXT IEMs sounded much more lively, more like wearing full size cans. But then when firing up some hip hop...holy crap. I mean, just night and day. It's the best listening experience I've ever had with hip hop without an actual subwoofer. I am really quite impressed.
I am considering having them reshelled as custom, as I mentioned (I did eventually hear back from UM on that). I had planned that next year I would bite the bullet on JH Jolenes, but now I am not so sure. It really is a unique experience for IEMs.
That said, I really don't like the new UM cable. I do have a couple extra cables for my Merlins that will work with them, but the new cable has that big bulky connector which is annoying, neither the iems or the cable are labeled R and L, so you definitely have to pay attention when you're connecting them up, and the universal versions are powerfully ugly. The design on the one that doesn't just say UM is really weird. Like a cross between a weed, a dragon, and an old school tribal tattoo.
My initial impressions are pretty positive. I like them a lot more than I expected, that's for sure.