Levoit is one of the best air purifier brands with a certified True HEPA filter. To be graded as a True HEPA, this air purifiers need to pass the test of U.S Department of Energy, and can clean at least 99.97% of airborne particles as small as 0.3 microns in size.
Instead, air purifiers are designed to be used for continuous periods of time. Humans, pets, cooling and heating systems, as well as open windows, constantly introduce new contaminants into the room. So the most optimal solution would be to run your air purifier 24 hours a day.
Levoit is a few air purifier manufacturers that only use physical filters and don't use any electronic air filtration methods that are responsible for producing ozone. Since they don't use other filtration rather than a 3-in-1 mechanical filter, Levoit air purifiers are also cost-effective comparatively