Handwalk/Roadwork vs treadmill
I always believed handwalk or any kind of roadwork (biking, free running beside a car, jogging/running, etc.) is superior than any kind of treadmill work unless you wanna do a full out sprint & don't have the space for the dog to run or if you live in the city and have only have a small area to walk your dog.
Sometimes it boggles my mind why some people walk the dog for 30-60 minutes or even more then come home and put them on a slatmill. It's the same exact thing. Why not just continue walking them for longer distance/time and skip the treadmill work (again unless you wanna do a sprint workout).