The Dual Footswitch can be used with the Big Bang, TA 501, TA 503, MoMark LMK and Studio Pre.
For the Big Bang Head one button on the Dual Footswitch controls the mute function (allowing you to tune silently), and the other activates the filters section, for TA 501 and TA 503 heads, one button controls the mute function and the other activates EQ bypass.

The same pedal, used with an LMK, gives you an on/off switch for each channel of the amp.