Many people do not understand why the Britax Marathon 70-G3 Convertible Car Seat, Onyx is called a convertible car seat when it obviously does not look like it can be converted to anything. What they fail to realize that it is not literally a convertible but instead, a car seat that adapts to the changing needs of the user. This is a truly wonderful car seat that guarantees safety for children. You can have peace of mind that your kids are protected well thanks to the Britax Marathon 70-G3 Convertible Car Seat, Onyx. This is truly one of the best car seats in the market. Made from durable materials and featuring a wonderful design, this car seat will definitely keep kids, safe, comfortable and relaxed at all times.