You should really compare it with the cost of getting specialist help to treat a bad back after you're 40. It's unlikely to be less than $70 a year, and it will likely go on for more than a decade.
I've had my Embody for just over 10 years now. It's been great, but the back doesn't go vertical enough for me (it's fantastic for slouching though). The plastic "springs" are starting to squeak with age. If I had it to do over, I'd have gotten an Aeron.
The right chair will definitely help. The few times I worked from coffeeshops for a whole day, or at the kitchen table with a regular chair, my back was killing me by the end of the day. When I got a 2nd-hand Herman Miller Mirrah the improvement was massive and noticeable in a very short amount of time. When I moved to the current Aeron I didn't notice any difference right away but in the last year I started feeling crap again.
You should really compare it with the cost of getting specialist help to treat a bad back after you're 40. It's unlikely to be less than $70 a year, and it will likely go on for more than a decade.