HHO kits are against the law of The law of conservation of energy.
Few points form there website(Ecofuel).
Hydrogen kit is a device which can save 20% to 40% of your fuel. All engines can only burn a small fraction of the fuel, the rest goes to the environment as exhaust causing pollution. HHO gas kit helps the unburned fuel to burn efficiently which not only saves fuel but also increases engine power and torque. HHO kits are suitable for all types of engines (EFI / non-EFI) and transmissions (manual / automatic). This can be installed without any modifications to your car.
Not possible, It can't save fuel, since it Increase the use of fuel to break Water.
This hydrogen generator, generates hydrogen and oxygen gas and this gas not only saves fuel but also it cleans the engine from carbon deposits, called HHO carbon cleaning process. HHO gas causes no harm to either engine or the battery.
No abjection apart from engine cleaning and saving fuel.
This kit draws current from the car’s generator (dynamo) and uses it to break water into hydrogen and oxygen (water electrolysis). HHO gas is then introduce into the air stream going to the engine.
Since it uses the power from dynamo aka generator or alternator, it is using the fuel power, the alternator is using the power (Mechanical From engine and convert it to electrical current), More current = more load on engine = More Fuel.
Hope i have cleared the question, Any questions regarding it are welcomed