It looks really uncomfortable to me.

Straps holding it in place, only two pads beneath your butt and no back support.

Maybe in a two minute demonstration it's ok, but wear it all day and I bet it will feel like a jail.

As for the assembly worker video example, it doesn't seem like a well-thought use case.

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

Also, off the top of my head:

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

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

How easy is it to put it on in a slightly incorrect manner and twist and break your leg?