I spent the extra $$ for nology coils and say no difference except for a lighter wallet.
So often is the case with these type of things. I've always heard the term, GOLLYWHOMPER used for the sort of items that are supposed to make your bike/something go faster, get better gas mileage, jump higher, and all the makers claimed what-have-you's.
Let the buyers beware especially if you aren't having an issue with a bad coil in the first place. I do believe in upgrading any parts needing replacement with better quality, if it's available.
I purchased a Parabellum windscreen for my bonnie and one of the factory claims is better fuel mileage. I didn't see any increase in their MPG claims but it did do the job I wanted it for, that of blocking wind.
Them 'ol advertizing people and some salesmen(AKA, "Scoundrels") will say just about anything to separate a man from his money, always have, always will.