The Advocate CS is one of 4 high-capacity convertible car seats that Britax currently sells. The others are the Britax Marathon, Britax Decathlon, and Britax Boulevard. The Marathon and Boulevard are also sold with CS (Click & Safe). From what I can tell, the Marathon and the Decathlon have smaller bases for installation in smaller vehicles. The Decathlon has an infant body pillow and multiple buckle positions, but otherwise, it is similar to the Marathon, including height and weight ratings. The Boulevard and Advocate CS are very large yet still have the same child size ratings, and include what they call True Side Impact Protection. The Advocate CS is their most advanced, and expensive convertible, because it adds Side Impact Cushion Technology.