Figured out how to encourage the cats to use this toy. Place it halfway underneath a bit of brown wrapping paper (or newsprint) that comes in your amazon packages. Irresistible. They like to push the ball under the paper and then sneak up on it, making the paper crinkle.  One of my cats can't resist making the ball disappear under the paper, he gets obsessed.  (Also helps to put it in the closet for a few days. Cats are just like kids and are interested again after a break.)