The device is essentially a compact electrolysis machine that produces hydrogen to feed into the inlet manifold of a combustion engine. Simple concept, as hydrogen burns very clean and aids in the efficiency of burning other fuels.
The problem is producing enough hydrogen that you need to get the claimed benefits from the hydrogen rich intake charge. In all the times I have seen electrolysis in action, it takes a hell of a lot of energy and a fair amount of time just to fill even a test tube with enough hydrigen to go 'POP'. This guy has either found a way to break the first law of electrolysis 'the amount of seperated elements is proportional to the current applied' or he has found a way to generate massive amounts of current in a compact box without it melting.
The other thing that concerns me is that he is not interested in just selling his product for a profit, he wants a percentage of the fuel savings that company gain from installing the devices. And also on top of that possibly gaining the carbon credits that are used in the Kyoto Protocol. When you start playing in that arena, it certainly doesn't seem like he is searching for a way to improve the environment or just run a successful business, he wants to take over the world.
The feeling of doubt isn't improved when you read the following:
What's more, even after the hour-long drive from Montreal, the tailpipe was not hot. In fact, we could wrap our hand around it without getting burned. Williams claims this proves that hot polluting emissions are not coming out of the tailpipe.
All that proves is that the surrounding air is cold. Your exhaust gets hot because there is fuel getting burnt and the hot gasses exit through the exhaust, adding hydrogen will make it burn better, not colder.