[Guvante]

> Why not use a stool? Cheaper and might have some back support.

Look at what the guy is doing. A stool will probably only cover 30% (if that) of his work.

> What happens if you forget and lean backwards, even a bit ?

What happens if you are on a stool without a back and lean backwards?

> How much time does it take to put it on and take it off?

It sounds like you only put it on once per day and just leave it on disabled without significantly impacting your movement.

[snowwrestler]

If you lean back on a stool you will kick your legs out to cancel the momentum. It's an unconscious reflex. Can't do that if your legs are strapped down though.