Its a controlable fuzz box, they were the dogs b******s back in the 70s,every steelie got one but didnt know what for

. Used properly it was possible to get a string effect, loads of reverb unison strings, when well recorded it could fool some.
Used incorrectly you could sound like a rocker with an overdriven six string.
Fun to have and a collectors piece now days.
Clarke Steel Guitars built them in as a permanent fixture.
Dave.