Reply by renners

I wouldn’t have thought adding $200 for metal hinges in a specialized chair like that would be a problem.
Anything produced as an aid for people living with disabilities or medical problems are priced at a premium anyway – just because they’re not mass produced in China.
Those hinges look perfect for that application, whilst the plastic one are attractively priced, are they worth taking a chance on when you know there are more robust ones available?
Of course the thing to do would be to try a pair – If they are adequate for a normal size person, you could always put a disclaimer on the chair (Not to exceed 180lbs etc.,), If you are making one for a super-obese person, use the metal and price accordingly.
Just a thought.

-- Do or do not, there is no try