New here, because I wanted to wait till I bought one to comment, but I wanted to clear something up.
Oxygen is not a fuel. Oxygen is an oxidizer that is used in the exothermic oxidation (burning) of a fuel. You need to add gasoline (or some other fuel) to the oxygen to burn more fuel. If you do not add more fuel, you end up with a lean situation where fuel burns faster and the overabundant oxygen endothermically (absorbing heat rather than creating heat) reacts with other gasses in the air like nitrogen, creating oxides of nitrogen. These pollutants combine with water and create acid rain. If you operate like this, it violates emission standards and is illegal.
Cold air intakes tend to register an insignificant impact on fuel economy in standardized government testing. While they may reduce airflow restriction at the air filter, modern cars adjust based on data from sensors to add more restriction at the throttle body to keep the air/fuel mixture the same. The impact on pumping losses for normal driving is minimal.