There’s an old thread on HN that’s quite informative.
I bought one of these a couple of years ago. It was £150, though. It weighs a ton, which is great for stability, and can be adjusted in half a dozen ways.
One of the reviews says it’s wonky. It is. The seat is very flexible. That way, it moves with you. It takes a day or two to get used to. I’ve had back issue caused by bad seating in the past. I’ve had no back or leg issues with this chair.
The things I’m sold on for an office chair are: lots of tuning options; great lumbar support; the wonkier the better. If you can justify it, get an Aeron (or similar).