There is so much bunk science on the internet on this stuff its not even funny.
Truths:
1) The basic technique for generating the hydrogen is electrolysis.
http://en.wikipedia.org/wiki/Oxyhydrogen In actuality you are generating oxygen and hydrogen. Follow some of the links for the science behind it.
2) This gas is generated in a perfect stochimetric ratio - that is 2 hydrogen atoms for every one oxygen atom - the correct amount needed to burn. If this gas is injected past the mass air meter, you should need no additional air to burn the hydrogen injected.
3) You can make one of these yourself for less than $100 bucks with some pvc pipe and stainless steel plates, and heavy gauge wire. Just google hho generator
4) I've run the numbers, a system drawing 100 amps, which this system does not appear to, gives the equivalent btu content of 0.03 gallons of gas per hour. Unless there is some black magic going on in the combustion chamber, i'm not buying it.
5) I have yet to see anyone publish test results on any device of its kind like this that wasn't along the lines of we drove the the car without the system and got x mpg, then we drove it again and got y mpg. No long term statistical averages, no documentation of control parameters for testing, etc. Do you really think the durango gets 9 mpg without the system? One isolated test proves nothing.