You have to use a great deal of caution when hearing a manufacturer tout the aerodynamics of their product. Reducing drag is a complex problem in that there are a variety of factors that affect it such as wind speed, yaw angle, as well as the shape and angle of the product itself. When you read that a product is the "most" aerodynamic this may be highly conditional, and of course the manufacturer is going to use the data that is most favorable. Whether or not this data is applicable to real world conditions is another story.
What makes the Abus Gamechanger helmet unique is that it addresses aerodynamics in a variety of different positions beyond just a level head. The "tour" position is mostly a mostly level head whereas the "sprint" and "race" positions are designed to reduce drag in a more dropped head position (chin down). The helmet has one of the highest ROI's when it comes to cycling aerodynamics in that it represents a lot of frontal surface area but it still relatively cheap when compared to a bicycle or wheel set. And that last thing you want when sprinting out of the saddle for the finish is a helmet that is slower in a dropped position. They also address the drag coming off the chin straps with a system that contours the face more closely, and a fit system that addresses head shape more accurately.
Most helmets tout comfort, ventilation, safety, and aerodynamics, and the Gamechanger covers these other aspects very well, but having a slight aero edge in a variety of positions may be just the advantage you are looking for.