When I fed kibble (I feed raw now), I always free fed - and my babies never overate, so it's a really nice option for puppies.
As for never switching, personally I think Hills is one of the poorer foods on the market. Also, keeping your dog on ONE food all of the time can cause acquired allergies. Variety is
good for them - and it is not always true that switching between a few brands causes upset. Humans don't eat one kind of cereal for every meal, day in, day out. Carnivores in the wild don't eat the same exact thing day in, day out.
There are a lot people on YT who will alternate between a few bags of different quality kibbles - and this is actually very good for these babies, imo.
