Octane boosters, not lead or even MMT, work by averaging your octane.

IOW, if your gasoline has 92 octane and you put in 16 oz of booster with 115 (for example) octane you get a miniscule bump in octane.

You can do better, and cheaper, by running Ketone or other high octance hydrocarbons in your gas. Heck a gallon of Methanol or better yet ethanol will do more than a bottle of octane boost.

Lead, and to a lesser extent MMT, work differently by chemically altering the gasoline molecule to make it more resistant to lighting off, not by raisng the octane level though the effect is the same.

Octane is rated on a special test motor that can vary the compression ratio. The difference in MON and RON numbers is the temperature of the air charge coming in, essentially.