This little gadget looks like the key you use to open your gas meter box.
Actually, the Option Knob enables you to control any of your pedal's pots with your feet. You take the existing knob off your pedal, put this in its place, and the wings then let you turn it with your foot.
There are two sizes: Classic, for most standard pot sizes, and Boutique, for pots with a larger diameter.
Simple yet effective idea.
Not cheap for a small piece of moulded plastic.
It's fairly primitive, but we can't dispute that it works.