We started with the Hi & Lite harness when he was a baby, but once he outgrew that we decided on the Flagline. It is really easy to put on and adjust and Fin has no problem wearing it for long walks. He is almost 6 months old and about 55lbs and the small we bought over a month ago still fits great and doesn’t pinch, pull, or bunch up on him. He knows when he has his harness on that we’re going on an adventure! I highly recommend!!!