Aren't all HEPA vacuums the same?
HEPA or "high efficiency particulate air" filters (defined by the U.S. Dept. of Energy) are known to improve indoor air quality (IAQ) by removing over 99% of dust, allergens, and other airborne particles down to .3 microns in size.
When comparing HEPA vacuums, you must also consider the way in which the filter is housed to support this ability. While all HEPA vacuums work to provide a cleaner environment and improve IAQ, there are a variety of HEPA classifications they may fall under.