Just got the Ier-z1r, comparing it to my Solaris 2020.
Two very different styles, the z1r has a thick, warm sound and has a good longitudinal soundstage. The bass is very strong, and the sub-bass is equally powerful. The treble is also good, no sibilance, good extension, but there is a significant gap compared to the bass. In fact I think this is both its strength and its weakness. The overpowering bass enhances the overall ambience, but also obscures the performance of the midrange and treble, leaving them with a noticeable drop-off compared to the bass. Overall it's an interesting iem.
The Solaris 2020 is bright and thin in overall style, with a more balanced performance compared to the z1r. The Solaris bass is not as powerful and substantial as the z1r, but its natural and realistic performance fits quite well with the midrange and bass. The soundstage is also smaller compared to the z1r, but once again, its a natural and harmonious match to the overall sound.
That being said, I still prefer to use Solaris. I prefer the bright and natural feel. That natural feel is not even found on some of the more expensive iem's (like 64 audio U18s), which is why I love Solaris so much. It doesn't necessarily compete with other IEMs in certain metric, but when all the elements blend together it is so natural and balanced. The z1r can be an antidote when I suffer the consequences of hedonic adaptation, but Solaris is my one true love for sure.