When I moved to different office last year, we were all given Mirra chair (another model by Herman Miller) and I can attest that they are EXTREMELY comfortable. Earlier, I used to get off the chair to catch a break but these days, I get off from my desk when I want to not because I am tired of seating in the chair. The chair's build quality is excellent and I can see that this chair can easily last 5+ years.
I have decided to buy Mirra for myself at home, the basic model costs around 600$, which is a small cost if it helps avoid problems with back injuries/fatigue.
But which would you rather do without?
I'm really curious if the investment in something even as high as a mirra or Aeron is really worth it, though, to be fair, I've never sat in either.