Gorila

I`ve just bought an ION, and somebody told me that if my air system does not have on/off, my ASA must. Is this true? I don`t know a thing about them. Do I need a drop to screw my ASA on it? Is there a good on/off ASA that replaces perfectly (no other piece, drop or rail needed) the original ASA?

I need some advice here, I`m clueless.