agree with chicpea - thye shouldn't have it most (if not all) are dairy intolerent.
Also cat milk is a con - cats can't have milk (mostly) so to make it digestible to cats they basically have to take everything out that makes it milk. SO you are paying for milky coloured water with vitamins in. Unless your cat is ill or not getting a proper diet there should be no need for vitamins.
Reason no. 283 as to why I hate whiskers.