Rapid-Rise is actually not a bad idea in concept because it is supposed to allow you to downshift easier under load. However, because of the way most index shifting designs work currently, this means you can only downshift one gear at a time. While this may be okay for the really experienced racer who would prefer to be able to upshift multiple gears at a time, the typical mountain bike rider will oftentimes find themselves in situations where it is more desirable to downshift a handfull of gears at once.