Sometimes you just need to put two guitars into two amps and be able to switch between all those things yourself. That's just one of the situations this little AB switch is good for.
The Quad box supports two inputs - you choose which ONE of them is on at a time, either Input 1 or Input 2. Then the signal goes out to two other destinations (labeled as Amps) however you need them. The signal can go to Amp 1 or Amp 2 or to BOTH Amp 1 and Amp 2 simultaneously.
The basic way this works is to send guitar signal chain input to two amps. It can be two amps on stage with you, or one can go to the front-of-house sound system and the other can go to your amp. You can use the dual inputs to keep two separate instruments with their own specific signal chains (and accessories) separate from each other - I've used one input for an acoustic guitar signal chain and the other for electric guitar signal chain, for example, when an effect I use for electric guitar adds buzz to the signal that I don't want in the acoustic chain.
The footswitches are pretty basic and there are lights to tell you which combinations are active - the inputs are simple when the light is on, INP 1 is active; when the light is off, INP 2 is active. For the two outputs, the lights indicate on and off for each one.
This unit comes with a 9v battery but can run off any 9v power supply with a negative tip and at least 300mA.