Does it work as in "Does it create HHO?" then YES.
Does it work as in "You can double your milage!!!" then NO.
Just the sight of that website instantly screams SCAM!!
Just remember that seeing a few bubbling hoses in an engine bay does not mean it has doubled the milage.
As for some background, this one sums some things up nicely IMHO:
Run your car on water? - it's a scam!