The RT-2 is a very small device that is designed in order to keep your dog containted in a designated space “inside” your home.
The TS-4 is for larger properties than the TS-5. This also has lights to show you everything is work properly, and an audible sound to alert you of any malfunctions.
The DG-9XT is designed to handle your very large, stubborn and “tougher-to-train” dogs. It works great on dogs that are considered “runners” or “high prey drive” animals that love to chase things (Huskies, Shepherds, Malinois, etc)