as sweet as that may sound, if the amp does not come with a foot switch, it's probably useless. unless you wanna pay someone to do the switching. remember, metallica has sound engineer, you don't.

playing metallica will definitely require a switchable distortion/overdrive unit. plus, i've figured that metallica is not really about gain. i believe MT-2 is more than capable for metallica than ML-2(this is the metal core, right?).