Got my universal MESTs in.
First, they seem comfortable as the shell fits well in my medium ears. I don't see any comfort problem here, but I'll need many hours of wearing them to be sure. (My CFA Solaris 2020s I can wear for literally 10 hours plus without any issues).
As for SQ; right away I'm hearing good things (a lot of air on top and treble detail/sparkle...but not harsh or too bright, and an even, balanced sound for instance) which is very good as I usually can literally tell if I'll like gear within the first 10 seconds of listening. I may not ever come to love gear that I like right away, but I've never even come to like gear that I didn't like at least somewhat upon first listen. So I'm set to at least like these.
But I'm very much going to be doing a lot of tip rolling since I'm not yet (with the stock tips that came attached to the MESTs out of the box and a pair of Final Audio E-Type tips I've been using with the Solaris 2020) getting the great seal that I do with my Solaris 2020s.
Much, much more listening...
EDIT:
Couple of (tentative) SQ notes: wow, the sub-bass on these! (with a good tip seal at least) I think it's more than on my Solaris 2020's, but that could be because on the Solaris the sub-bass is more covered over by the (imo) excess mid bass. On the MEST you can hear it more distinctly...also there is more bass texture and definition.
Also noticing great detail on these from top to bottom, good/great micro detail and lots of shimmer/sparkle/air at top (with being fatiguing to me) so I can hear more nuance in cymbal work for instance, as well as great overall layering and separation. Vocals are slightly upfront, but not as much as on my Solaris (which is both good and bad depending on how much you are a vocal head...I lean towards being one).
The overall presentation is somewhat light, airy, large, but not too thin or weak, with a crisp but also natural tone with just enough weight in the lower/mids to keep things from being too anemic (at least so far: haven't tried my overly thin test recordings yet). It's quite different than my darker, thicker, warmer Solaris 2020s. It's certainly not as forgiving of lesser recordings, more transparent, though I feel that the Solaris also changes tone with the recording to reveal the distinctive production.
The contrast with the Solaris is large, but I'm not one to really react positively or negatively to such contrasts as I think of transducers as having different flavors and I regularly shuffle between them (such as going through my different headphones and speakers semi daily for different applications).
Also, these seem to need a lot more volume than my Solaris.