Has anyone got any experience with fitting a hydrogen system to their car or van?

I'm thinking about buying one of these http://www.hho-plus.com/product.php?id_product=11 the only person I know with one locally tells me they are the best thing since sliced bread. However everything he buys is always the same therefore I take everything he tells me with a pinch of salt.

It does seem an interesting way to increase the fuel economy it return for a few 25 litres of water a year.

My current truck runs at about 10 litres per 100 Km, 30 to the gallon, a saving of 30 plus % would be good.