I noticed the most active section of Headfi for IEM discussions didn't have a UM thread, so I asked UM if it would be OK to start such a thread, and here we are. On top of having and loving both the OG MEST and MEST MK3, I also have their 3DT triple dynamic driver IEM, which isn't as good as the other two, but it's nice in its own right, with an awesome soundstage. Soundstage seems to be something UM is good at, based on my experience with three of their IEMs anyway.
Something I really love about MEST MK3 is how much vertical space it has. It really fills up that space too, making everything sound BIGGER in relation to my more conventional IEMs. I guess it's that BCD at work!