Hello I will help you with your question,
A gimmick that is supported by a little science but physics get in the way of them actually working.
The claim is that adding the Hydrogen (or Brown's gas) that is produced to the intake you get a magical boost to combusting the gasoline and the gas so you get incredible mileage.
These have been tested by the US department of transportation and found to have no value.You cannot get more energy out than what you put in so the alternator producing the electricity that causes the hydrogen to be produced uses more energy from the fuel than you get back in burning the gas.
The kits do make changes to the oxygen sensor inputs and the intake air temperature sensors and that causes the engine to run lean getting better mileage but long term the engine is hurt by the lean running.
If there was a way to get better mileage the manufacturers would have put it in their systems so that they could sell more cars with the ad stating you get 40% more MPG than their competitors.
Please let me know what I can do to help you with this
Every one is a gimmick, for that much money you can buy a lot of fuel and not hurt your engine and exhaust system. They are like the platinum fuel savers, acetone in the fuel tank the 200 mpg carburettor that the oil producers were keeping off the market back when cars had carbs. No free lunch and if there was a legitimate way to increase the mileage the car manufacturers with their multi million dollar engineering departments would have incorporated it in their vehicles.
Backyard Bob did not discover an amazing fuel saving device that he can sell to you that has not been tested and debunked.
Try Snopes.com or just google "Brown's gas scam" and you will have more reading that you can digest on the subject.
Please save your money and let me know how i can help you with this
Another part of the problem is the volume produced. It would take an incredible amount of electricity to produce enough gas to run the engine. That is the stumbling block of conventional hydrogen vehicles, a car cannot carry enough to get the needed range and refueling the high pressure tank required takes a very long time. It works well in a bus system if electricity is local then the bus can have a very large tank.
With the sites you will find by putting "scam" after "browns gas" or "HHO" you will have hours of reading from reputable sources that will explain in detail why it does not work.