Using this for my very active 35 lb Border Aussie. We walk 30-50 miles per week depending on weather and daylight. She's very comfortable wearing it. I use the leash connector on the back because she's not usually a puller. She loves searching for rabbits and we pass a lot of places where they live.
It's beautifully made and quick to put on or take off. It replaces a Ruffwear harness that worked pretty well but had four snap buckles instead of two.
My only complaint is that the buckles are much stronger than they need to be, making them tough to unhook, especially in cold weather.