From the web site:
The HHOS has been tested in two different vehicles (the current prototype, which is a 1994 Ford Escort Wagon, and a 1998 Ford Ranger pickup) and fuel economy increases have ranged from 22.9% to 100% depending upon the amount of electrical energy (amps & volts) that are available for the production of Aquygen™ Gas.
Looks like the details aren't as impressive as the video.