It is basically designed to catch the cooler air passing through the hood, and if placed correctly would help cool the engine down faster. It is usually placed at the point in the hood where air pressure is the highest in order to catch the most amount of air.
Materials also differ from ABS, to fiberglass and carbon fiber. As usual Carbon fiber would be the lightest but also most expensive. Improvements on performance highly depend on the hood scoop's design and positioning.
The additional performance boost would usually be felt at top speeds that's why it is primarily used in racing.
If you do have the extra cash, you may want to get this additional upgrade.
