The companion to the DMC GCX switcher and also phantom-powered by it (or the multi-talented Axe-Fx), this was the industry-standard for years until it was superseded by the bigger and more powerful Ground Control Pro.
This one has the upgraded chip in it so it can control up to four GCX‘s like the Pro, but I keep it becuse I prefer its smaller footprint and it’s smaller and lighter to carry around.
It is connected to two Boss expression pedals. whichever device(s) I have it controlling, the second pedal always controls volume pre-delay/reverb (to keep the tails when the volume is ducked). The first pedal controls whichever is the most important parameter in any given patch (eg effect depth in a chorus patch; rotary speed in a Leslie patch etc).
I also like it because it is the still the only floorboard with a really big display that you can see from a distance in almost any stage lighting conditions.