They have no gap growth over 100k miles, so yes they are extremely durable.
Have you ever tried removing a spark-plug that’s been in an engine for 100k miles??? I’ve done it once and won’t do it again…Of the 6 plugs removed…two had to be helicoiled (especially dangerous with aluminum heads).
A lower voltage and higher flame does NOT mean better performance or better gas-mileage…nor does it mean it’ll burn more fuel.
Believe me, automakers never want to pay more for any part, when they do it is because there is a real performance benefit.
The MAIN reason is because of longevity…PERIOD…Performance - Marginal at best.
As for Auto-lite plugs…While I never had a problem with Fram filters…I’ve had MAJOR problems with Auto-lite plugs…They are by most people I know to be the low-end of the low-end plugs. If you want the cheapest plugs available and don’t car about your car…buy Auto-lite…The difference between Auto-lite plugs and NGK is about the same as a Rolls Royce and a Pinto.