Ha, yeah you can make hydrogen and oxygen that way but the you can't make enough to make a huge impact on large engine efficiency. And to make enough gas for a large engine would require massive amounts of electricity. Scientists have been making hydrogen and oxygen that way for over 100 years but the system is designed for quality of materials not quantity of materials. But I wouldn't completely doubt ALL (or at least question the amount of mileage gains) of the claims because I have seen it work on
small applications.
The only reason I would buy it is if I could sue them for making such exagerated claims.