Reading the EPA 511 standard (found here http://www.epa.gov/otaq/consumer/b00003.pdf) reveals that the EPA is ****ING STUPID. The Blade can make the claims that it does because it takes advantage of a loophole in the EPA's testing standard which dictates its procedures measure CO2 output to determine gas mileage for devices that are primarily designed to filter engine exhausts (Page 6, "...carbon dioxide which is the primary constituent in the fuel economy calculation.") They basically measure the amount of CO2 that is emitted from the car, and stoichiometrically calculate how much fuel is burned and compare it to how much the wheels moved.
The problem with that test criteria is that it doesn't take into account that this device could be (is) absorbing the CO2.
The EPA requires that a followup test be performed (Known as the HFET) when improved gas mileage is claimed, yet the mention of these test results are strangely absent from the Blade's page.
Save yourself some money, and spend the $200 on gas instead.