I don't know why but I was intimidated by this one. Maybe the unusual key input, I don't know. But I had the parts for 6 months until I decide to build it.
Works on first try but I'm not able to test the "Key input" yet...
Plug your guitar into the Key Input, run a patch cable from the Key Output to the normal Input of the pedal, then from the normal Output of the pedal to the front of your amp.