NOS, Torco, and Lucas brand octane boosters all use MMT. They work and work well. They don't hurt anything 'internally' either. MMT is a very effective octane booster. I got a killer deal on a case of Lucas and am using it in the Mustang currently for piece of mind.
Besides MMT based stuff, Xylene/Toulene added to gasoline works great as an 'octane booster', as Xylene is around 116 octane and Toulene 114 if I remember correctly. Adding a gallon of either to 3-5 gallons of 93 dramatically raises the knock resistance.
Used both personally on previous and current cars. Happy with both results. Xylene/Toulene is a bit on the expensive side, but if you need high octane in a pinch and there's a Home Depot near by it works.
