That kit contains an electrolyzer, fuel heater/ionizer, fuel additive, and an electronic controller that tunes the emissions control system that controls your engine. Without the electronic controller, it's impossible to tune the engine to accept your mileage and your computer will "learn" around the added efficiency. Thus you will get good mileage at first, but eventually your ECU will force it's hand and you'll get the same mileage as before.
The computer is programmed for a stock engine with stock efficiency. If you make the engine more efficient without telling it, the ECU will do all it can do to get back to the stock parameters and stock gas mileage.
Now, I'm not saying that a simple hydrogen boost system won't help at all by itself. But I am saying that there is much more to be gained when you are able to tune the emissions systems.
Having said all of that, if you are a DIY kind of guy and don't want to spend a lot of money, you can "tune" your ECU manually, usually using resistors over all of your engine's sensors. Note, however, that to keep the ECU from learning around them, you have to modify all of the signals to keep the computer from getting confused and either tripping a CEL or ignoring your modified sensor. Read about tuning for mileage in the following links:
You should also consider that the O2ptomizer (the electronic controller in the "kit") takes these methods a little further and adds the ability to modify time-sensitive signals. In other words, with these simple mods, you have to worry about cold-start issues; with the O2ptomizer you don't.
The combination of fuel heat and ionization, hydrogen boost, and tuning have resulted in substantial gains in mileage. The minimum seen is 50% improvement. Numerous vehicles have doubled or even tripled their current mileage. With hydrogen boost alone (done by a gentleman on this forum) the max gained is around 30% (which will greatly depens on the vehicle).
Going further to answer your question, do a search on this forum and you'll likely find some of the best designs for hydrogen electrolyzers on the planet. Some have achieved "over unity" production when combining their electronics with a well-built and designed series cell. You'll likely be able to find a plethora of information here on the forum. 
Statistics: Posted by Pinhead — Sat Mar 08, 2008 12:18 pm
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