If they work the way I think they do, they work like an Reverse Osmosis bladder tank.
In that scenario, I doubt brand has anything to do with it. Size matters.
Watts assembles alot of the home RO kits people have.
My guess is Watts is an OE maker, and possibly so is AO Smith(they have a huge factory, and got Sears Kenmore), but being this isn’t a device that your drinking out of per-sea it could be outsourced to some scary factory 10K miles away.
I am doing my install tomorrow, I will let you know what ended in mine.
Also anyone know how an expansion tank is tested? My house did not come with one, my dad said not having one will make your pipes shake, I have heard that.