First is costs and then simplicity of use. A “trolley” type system uses a cable and wire (or cord) to support the retriever and operate the carriage down the range and back. The motor housing to run this system is generally located in the shooting stall over the shooters head and is operated by a simple switch. The pros to this type system are simplicity of use, easy maintenance, longevity, and cost effective. Cons include replacing cord and/or cable if accidentally shot, and lack of any technology such as preset distances, etc.