forgive me for not having watched the videos to see exactly what their idea was... but if it's about electrolysing water into hydrogen and oxygen just to burn the mix in the engine, there's a major problem with that... the load it puts on the alternator puts more resistance against the engine and you end up not even getting that much energy out of burning it back in the engine.
The only way that it can work is if the electricity for it doesn't come from the alternator in the car... so solar panels might work, if you can put enough of them on without hurting your aero-dynamics too badly. The more feasable method to me though, would be recapturing heat from the exhaust to power a steam turbine to produce the electricity (note, you have to use the heat from the exhaust and not the exhaust itself for this, otherwise you end up in the same place as you were with using the alternator). A final option would be using much cheaper home electricity to produce the gases, then store the hydrogen in a compressor tank that you then move to the car when you take a trip. This doesn't help you get energy for nothing, but does let you use cheaper energy sources to power your motion.
Of course, it's much simpler to make a few tweaks to your vehicle, and you'll see MUCH better mileage. I'm talking about "tweaks" like inflating your tires to their max pressure... replacing your air filter with EVERY oil change... keeping up with oil changes, oh yeah, and if you really want to get crazy, lean out the fuel/air mix via your OBD II computer. Just don't lean it out too much, the compression will go through the roof and you'll end up blowing out a cylinder or two.