In the words of ThorpyFX:

The BUNKER is a MKII version of the Brown source drive pedal. It is smaller, louder and more tonally flexible. The tonal flexibility is provided through a texture control that allows you to have whichever type of drive sound you want from original Brown Source style drive through to thicker and more harmonically rich drive. The tonestack bypass is on a footswitch for two switchable sounds as well as a three way toggle switch for further tonal sculpting.