If you're going to try it, go straight to the manufacturer and save yourself $60.
Volo Performance - Chip Tuning Made Easy
Although most of the people in this forum think using HHO is crazy, I have seen some success with it. I'm not doubling my gas mileage like some people claim, but it does seem to allow you to lean out an engine more than with just gasoline. When I get a new car, I plan on getting my HHO system on a dyno for 100% scientific data. But I won't get into that right now.
I tried using a Volo chip with HHO and I got about a 10%-20% increase in MPG. the car I was using had some mechanical problems, so I had to shut the project down. But I did see some success with the chip. How the chip works, I got no idea. I also don't know how it would work without HHO.
I do know the chip you'll want is the FS3 and they claim 15-18% increase in MPG. If you're interested, I say order a chip, and do some ABA testing. All of us in the forum would like to know the results. Good Luck!