What
@coolblue is talking about is not that there is a coating, it's that people are worried about the color of it.
Your plugs have a coating on them now... it just isn't orange. If the effect of the octane booster was purple, we'd be having the same conversation... but if it was more brown/grey, nobody would be talking about it.
I prefer the octane booster route, because it's in your control as to whether or not it's going to work. When you start using meth or propane or water to bandaid your lack of octane, you runs risks inherent with bandaid systems. If you're using them to improve performance on a 93 tune, great, but I wouldn't recommend using them to grenade your motor when they stop working.