My cats also eat Purina cat chow and I feed them on the counter because I don't want the ferrets eating their food.  Not the best place to feed them but started doing so to keep the dog away from the cats' food now the ferrets.  The ferrets may eat a stray piece of food that falls on the floor but that's about it.  I feed them ferret food as cat food is for cats.  The problem I have is the cats will sometimes eat the ferret food that is in a couple bowls on the kitchen floor.  The ferret food is far more expensive than the cat food so I don't want the cats eating it.