Hello,
I start off all of my puppies with a collar when young. I leave a collar on for time for them to get use to having it on. I also start "walking" my puppies around INSIDE the house. I do this so that when we go outside for the first time, they are already use to having a collar on and understand about what is expected. They are much more likely to follow you around INSIDE the house then outside. So start inside. Unless I am going on a walk or someplace where I might expect some challenges, I just slip a collar around them and go. If I go to the vet, the dog food store I just use a collar.
But I do agree that in some cases, an untrained dog who pulls will need to be in a harness. A harness is a good idea.
Good Day~