My baby sister had this (and the Fisher-Price telephone) as a toddler, 50 years ago, and when she wasn't playing with one, she was playing with the other. The "doughnuts" double as teething rings, and can be used to teach children colors, dexterity, relative size (which is bigger, the blue circle or the red one?), coordination, and proportion, and the rocking motion of the base not only fascinates them, but teaches them rudimentary physics.
I have bought this product many times as a gift for infants and toddlers. It is a great way for children to develop their fine motor and problem solving skills and learn about colours, size and sound for instance.