Similar chairs to be honest. Aeron doesn't have adjustable seat edge. Aeron probably slightly better grade materials. Also aeron is mesh back, where the Mirra 2 is plastic. Although mine has the butterfly back upgrade which is like a mesh overlay on the back. Also arms adjust differently. I found a code and bought for £650.
I think some sites sell it for around this price anyway. Well working I think?
https://www.wellworking.co.uk/chairs-c2/office-c4/herman-miller-mirra-2-chair-graphite-triflex-p27
Thanks, I’m considering options for replacing my IKEA Markus. The only thing the Markus lacks that I’m missing is seat depth adjustment.