The restrictive properties of filters vary from brand to brand however reusable filters often block less air. They are cleaned rather than replaced which saves you money when servicing.
How to tell if your air filter needs changing? In order to get the most fuel economy out of your car the filter should be as clean as possible; hold it up to the light, if you can't see any light shining though it then its too dirty.
Follow this link to Find and remove your air filter.
The cleaner it is the more power your engine can create and the greater your fuel ecomony.