Gordon Loughton of 24 Freshfield Bank, Forest Row in London has a business (and another here)selling a miracle fuel saving product which he says can dramatically reduce your engine’s fuel consumption and improve its emissions using… by up to 30% apparently.
HHO is a scam product which cannot possibly work and which has been show to be nonsense.
Oxy-isolators , also called lambda sensors, are devices which fool your engine’s computer into making the engine run a little lean which can increase MPG a little but at the expense of performance and emissions (and it is probably illegal too).
Here is Gordon’s website
Here is why HHO is nonsense:
And here is a longer article on oxygen sensors, what they do, how they do it and why it is not a good idea: