Basically this is a kill-switch for XLR mic or line signals that supports phantom-powered microphone sources as well.
On the side of the unit, you can either select "Push to mute" that means you can switch your mic or other source on or off as needed. The other selection is "Push to talk" ( = commonly referred to as "PTT"), which means that the line stays open as long as you hold the button down. Anyone who's used intercoms or radio communication devices should know the principle.
The good side is that the unit is built like a tank. You can use either your foot or your fingers or maybe even your fist to control the switch. The unit is very rugged.
The switch response is also very fast, I would imagine that somebody would like to use this as an effect in their instrument/vocal rig (i.e. "Buckethead"-type tapping). The downside is that the mute is _not_ true mute. Instead of completely cutting off the signal, the level is lowered -60dB, which in high gain situations leaves the signal "leaking" through. So, you might seriously consider a noise gate unit to your signal chain in addition to this unit.