I'd never buy or use them, i'm pretty much set with NGK or autolite with running alcohol. I can remember many years ago when STP was sponsering INDY cars, there was a pic. taken showing some mechanics pooring STP in the engine and in themsame picture there was s drain pan under the egine catching it as it came out.
I agree with road kill back some yrs ago i tried a vertex mag, i was running a MSD 7 AL, the mag actually slowed dow the car a few houndreds. You only need enough fire to fire the plugs on your application. It's a little different with nitro because it's harder to light and keep lite
Zip.