Cat showed very little interest
The balls did smell very strongly of foam which I think didn't help. Initially the kitten did enjoy the balls - chasing and such like, but only really when they were being hit between two people with table tennis bats.
My kitten would initially chase the ball, but as soon as it stopped moving, she would stop showing any interest and walk off. It was very frustrating.
Perhaps it's my kitten - but she's a mau, and supposed to enjoy fetching. She did prefer a knotted plastic bag to this.