i'm avoiding spending time on mods that claim to promote more "complete" combustion based on info on http://fuelsaving.info
The unburnt fuel in the exhaust (even before the cat) represents 1 or 2% at most of the input fuel. If you factor in the energy in the CO emissions, the figure still only rises to 3% maximum. So even if the fuel "saving" device could totally eliminate unburnt fuel and CO in the exhaust, and give an absolutely 100% complete burn, you would only save 3% of fuel.
i believe this guy knows his stuff - he's a british auto engineer working in the industry with specific experience in engines.
nevertheless, before i read his site, i foolishly went out and bought a set of bosch platinum plugs. replaced an essentially new set of "regular" NGK plugs, and I now seriously doubt there's any difference between the 2 (other than perhaps service life).
I don't go for crap that promotes anything. I don't pay attention to websites that are paid by manufacturers or the government.
I only pay attention to real people with real cars.
I'm unsure if this is some "conspiracy theory" of yours or what... but if you would actually visit the site above you'd find out it isn't a government site. It's made by an automotive engineer, who worked in the industry for decades.
The only reason to go 1 heat range hotter is if they are getting fouled. One heat range is not a big jump. I used to run a hotter plug in front than the back in my v twin MotoMorini motorcycle as the rear plug and cylinder runs a little hotter than the front. Going too hot will cause pre-ignition and knocking at high speed and really damage the engine. So if your plugs are a little brown do it.