Defintitely do not need one for a puppy! I do not like the GL because it can cause neck injuries and the dogs generally hate it. I much prefer the Easy Walk body harness by the same company. However, since you have the pup at 9 weeks, you have the chance to teach it well from the start without any tools! If you need help, the no-pull harness is a better option than a head halter.
If you mean the head halter, I don't know anyone who would advise one for a puppy. If you mean the no-pull harness, I don't know anyone who would advise one for a puppy. Puppies need training before they would need a management tool like this.
I am getting a new puppy and I am trying to get information on the right tools to train him properly. We are enrolled in puppy classes but I don't want to buy a collar/halter/harness or combinations of those that I will not end up using.
That is what I am trying to accomplish -- "exactly".
The easy walk harnesses and halters are something you might consider much later IF you are having huge problems training your dog not to pull on leash. Read the information in the training section about teaching your dog to walk on a loose leash and you may never need on of those tools, just a nice flat collar. Time and patience and training are the best tools.
My 50 pound beast of a dog has never been a leash puller because, from the day we got him, we worked on training him not to pull. It is far easier to teach proper behavior from the start than it is to cure problem behaviors that you inadvertently let happen.
I put the Easy Walk on Hadley for 2 days. We walked for 16 hours in those two days. Now she's on her collar for the store. Most people would not need either of those for a puppy. For a puppy your best bet is to use the collar and when puppy pulls, you walk backward until they are back to you. Treat. Start walking again. Every step they are walking good, treat. As they get good, you reduce the number of treats.
Congratulations on your new puppy! And you're doing the right thing by asking about training tools. Start with a collar. He may never need anything else. The puppy classes (great idea!) should help a lot with training your dog to walk on a leash.