Check out the ingredients and the percentages on the chick starter versus gamebird starter. You'll see there is quite a difference.
You'll also find that keets have a much higher metabolism and will eat a whole lot more feed when confined than a chick will.
I fed mine gamebird starter and then got them free ranging as soon as I could. Otherwise they'll eat you out of house an home! Now that they're adult size, I don't hardly have to feed them anything. They scrounge all over on their own, sometimes go into the coop and help themselves, and will sometimes come over to the dishpan that I throw the food into for the ducks in the mornings and evenings. Mostly though, they just take care of themselves.