The stage one air cleaner is a high flow filter. Meaning anything that flows better than the stock filter is "high flow" Next you move into how much more air flow is possible. Here is something many don't realize. The engine sucks the air in through the intake manifold and throttle body. The air filter is designed to filter out dirt particles. They can be too restrictive and not allow enough air to pass. The stock air filter is designed to give just enough air to match the fuel and exhaust and meeting EPA requirements at idle and low RPM's. When us guys like to beef up the power, we increase the air going in and the air going out (exhaust). However, once you do that, you need more fuel or it will burn too lean and damage the engine. So then you add a fuel computer of some sort to trick the on board computer to deliver more fuel. Back to the air filter. A dirty filter may begin to restrict the air flow to a point of reducing power. So a larger filter with a good air flow path is better in any case. Manufactures like myself try to promote our filters as the best design for various reasons. Generally large is better. A smooth air flow path is also important. If the air has to make sharp turns it will slow down a little. Also, sourcing the fresh air away from the hot engine will deliver cooler (more oxygen dense) air. Finally and often the most significant feature of air cleaners is the aesthetic look. Wait there is one more....price. Most aftermarket air cleaners will deliver more air including the stage one. Some deliver more air and cooler air than others.