The pressure is still placed in the same areas, neck and chest/belly. You pull on the leash and the spine is forced into an unnatural position. GPs also have a high likelihood of "freaking out" while on a leash thus increase their chances of injury.
The top 3 pellet choices are
Oxbow Pet Products | Welcome Kleenmama's Hayloft :: Home (Oxbow is available in some feed stores and vet offices as well as online and Kleenmamas is only available online). If neither of those can be found or you won't buy online then Mazuri 5664, only get the Mazuri with that specific number after it as it's the only decent feed they make for GPs.