In fact it is not useless. And you can make your HHO simply by yourself from distilled water, and get 10-50 % more mpg using this method. Easy and simple. You don't need much hydrogen to use as a hybrid fuel to your car's engine, and it _does_ increase your mileage. It also cleans your engine while burning.
Have you tried it? Many others have, and it seems to work
. Really.
http://mikasf.water4gas.hop.clickbank.net/