Baoding balls

[Josh Young]

I know there used to be a martial art that used these tools.
I have some stone ones, yushi-jien-shen qi the box says.

They are easy to insert into taiji moves and to insert into my throwing training (I throw spikes, darts and impact objects and have for a few years now) however I have been able to find zero information about them being weapons except for a mention of them related to me found in a book called Chinese Hidden Weapons.

Are there any keepers of this art alive?