Ok well after owning these for a couple of months I feel a duty to report at least a few thoughts. (I don't think of myself as enough of an audio expert to give a full review) I owned the original UERM for about 3 years prior to purchasing these and absolutely loved their sound from first listen. With the UERRs, it was a little bit different. Everything seemed less, less soundstage, less transient amplitude, less dynamics. Initially I was a bit underwhelmed, but after weeks of critical listening, and retuning my brain, I'm starting to hear more details. Small subtle background sounds, things that I didn't hear in the UERM. Treble and bass extension, reach out farther and what seems to be flatter. I'm getting more used to the flatter frequency response, but there are still parts about the imaging that bother me. The UERRs appear to have really strong center imaging, and while this does help vocals and single instruments, to sound more focused, I feel that it makes the soundstage seem uncomfortably narrow. The UERM, had a massive, almost open back soundstage width that surrounded you with lush punchy sounds (although admittedly a tad bit peaky, and less extended) While this may have been less accurate, it made everything come to life, cymbals crashed with deafening attack, and snares exploded with a shatteringly crisp pop, that to me very well replicated the harshness of reality. The UERR in contrast, sounds very inoffensive, which is good most of the time, but sometimes gives a sense that some sounds are artificially restricted/smoothed over.
I fell in love with the original UERM, because of its wide soundstage and harsh, hold-nothing-back (realistic to me) in your face dynamics. All in all I'm satisfied with the UERR for what it is, an accurate, and highly detailed CIEM. In many ways it is an improvement over the UERM in terms of tonal accuracy and extension, and while I do enjoy listening to it, I can't help but feel a little disappointed that part of that original UERM character is missing. Once again these are just my humble observations, YMMV.