Carbon filters are used primarily to filter small pollutants such as smell, odours, mould and pollen. They are used with centrifugal fans, located within a growing area and exhaust air sucked through them and then expelled from the growing area.
Quality of a carbon filter is generally found in their origins - and CAN FILTER comes from Europe where high international standards are maintained and 100% smell removal should occur. Cheap filters may not ever achieve 100% removal.
Intake filters are higher flow and will not remove the smell, but are effective against insects mould and dust, but especially Pollen which can cross-contaminate a crop with an inferior type leading to seeds that are undesirable.
Bug net intake filters are just for insects and the most basic filter