Does anyone have experience with these slow feed bowls? They have pretty great reviews from what i can find. Im gearing up for a new pup, should be born about a week from now so we expect to bring him/her home in 9 weeks or so. Part two of my question would be, does size matter? Can i get the large bowl and allow the pup to grow into it? Or do i need a smaller one (medium), and then get the large in a handful of months?