Those extendable leashes are great for large parks or fields where you can let your dog out to the full length so it can run. I hate hate hate them in the city. For some reason, I run into quite a few people who walk their dog without the leash locked, and when the dog spots mine it comes running over, extending the leash all the way, and the owner ends up struggling to get control/yelling at the dog to return to them (good luck with that) while my (reactive) dogs growl and snap at it. I often end up way off the sidewalk, in the street or on someone's lawn, trying to keep my dogs away from the flexi-d dog.