Round-cylindrical breather — TA Technix

The sport air filter fits into the original airbox in place of the cartridge. Its mesh allows more air to pass through over the same surface area: the power gain is modest and honestly barely noticeable on its own, but it adds no cost, risk, or need for adjustment.

Its real benefit is economic and environmental: it can be cleaned and re-oiled instead of being thrown away. Over a car's lifetime, it costs less than replacing a cartridge every two years, and it affects neither the sound nor compliance.