

Fair, but do you have to manipulate them at the same time? Most of the time we use our hands to hold something, or do very simple repetitive movements. This doesn’t require much brain power to do, and is still very useful. For example, such arms could hold our bags, while our natural ones can do whatever else.
On an unrelated note: the site has the least invasive adblock banner I’ve ever seen. Made me wish to immediately turn it off.