The short answer is that they are dangerous.
I’ve never used one, however, one got tethered around my ankles while I was walking Paulie.
A few months after adopting Paulie I decided to go a different way since it had just snowed and was bitter cold. We were having a nice walk together, Paulie running through the snow like a puppy. We stopped for a few minutes to take care of business and I noticed an open garage door across the street. A man was working on a car so I paid no mind and waited for Paulie to finish. All of a sudden, I saw this little dog come barreling out of the garage with his retractable leash attached to his harness. My first reaction was to pick Paulie up and I would take the brunt of the impact. As I was holding on to Paulie for dear life, the other dog started jumping up on me then was running around my feet in circles. The leash was wrapped around me so I couldn’t move.
It seemed like a long time before the owner came running out of the garage to unwrap my legs from the leash. He apologized and all I could say was, “please get your dog off me.” At that point, Paulie was all fired up and I was upset and mad. When we arrived back home, my husband knew something had happened. It took weeks before I would walk Paulie by myself.
Another incident occurred at the vets office. We were waiting to be called and this lady would release the leash so her dog would have free range. As the dog approached Paulie, it was obvious Paulie was upset and started barking. The lady her dog was friendly. My response was that her dog was entering Paulie’s space and he wasn’t happy. I asked her to move her dog. The clinic now doesn’t allow retractable leashes and patients have to wait in their cars instead of sitting in the lobby.
I avoid pet owners who use retractable leashes.