For some reason my dog will not touch this toy if you put food inside it. Without food he will happily chase it for a little while if we throw it for him but then he goes to find his lighter, more flexible balls and brings them to us instead.
The toy is indeed made of robust rubber yet it still has some give and will bounce around a bit if thrown. It is designed to be filled with snack treats although mine came with the hole at the narrow end partially sealed so I had to struggle with long-nosed pliers and scissors for ages to open it up properly.
Unfortunately my Staffy has been remarkably disinterested in it even when it has peanut butter inside it so it lies unused most of the time.