Gimmick spark plugs have been around as long as I can remember, and I've been tinkering with engines for nearly 60 years. They're equal parts of wishful thinking and outright lies. Like P.T. Barnum was fond of saying, "There's a sucker born every minute!" Keep the engine well-tuned and the spark plugs clean and gapped right, and any plug will give good gas mileage.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!