I think the window of socialization closes just as puppies get to start classes. I think they're a good idea for teaching people how to start training their puppies, and I think Ken is right about teaching them to ignore other dogs.
Personally it doesn't sound to me at all like a puppy class I would EVER want to take, and definitely not the way the puppy "kindergarten" I took mine to was run. We were definitely careful to match pups together and only if they seemed ok to introduce more, depending on age, and the instructors didn't even go into food or speutering. It was about teaching focus and starting basic things.