It looks like Aquatune is water injection. Water injection is used as an anti-knock and it's been used as such for 50 years or more. with water injection and fuel injection computers, the computer can add ignition timing and lean out fuel mixtures and get modest gains. 'Hydrogen branding' of water injection systems is Fraud against the unwitting as far as I'm concerned. As soon as I read the words on the front page about 'litres of hydrogen' produced I knew it was a sham.

Liquids are measured by volume because liquids are incompressible. A Litre of liquid water has a known mass and a known number of atoms. A Litre of steam (water vapour) depends on too many other data points, temperature, pressure (manifold vacuum) etc. but Chemists use "STP" Stanard temperature and pressure to make statements like the following:
"The volume ratio of liquid to gas is approximately 1:850"
-https://www.h2tools.org/bestpractices/h2properties

So, you're getting 1/850th (or less) of what is implied by their statement.

I can also state for a fact that it takes a great deal of electricity to make hydrogen from water and to compress the hydrogen into a liquid or high pressure vapour fuel so it can provide substantial energy for combustion.

Chemistry is a mass / energy balance and there are skills in analysis that should be available to most high-school seniors. I will do some hydrogen mass / energy calculations on my blog here in the weeks to come.