They’re called “Bao Ding” balls and they are used just for the sake of using them
they do help you with hand dexterity and are said to help those with arthritis or bursitis by exercising the joints of the hand.
probably more preventitive and seeing as many forms of arthritis and bursitis are viral, I doubt that they can do much for the acute versions.
They are relaxing to use though, swirling them in your hands both clokwise and counter clockwise does indeed help your dexterity. If they have the little chimes in them they are even nicer to play with.
when rotating them there are 2 correct ways either clockwise or counterclockwise while doing the following
1: keep them in constant contact with each other never allowing them to seperate or bang together
2: keep them from touching each other while you rotate them. the second is much harder and more advanced enjoy and good luck!