This is a super popular overdrive pedal and is used by such rock stars as Robin Trower and Mike Campbell and this is a great sounding example in great condition. This is what the  Fulltone website has to say about their creation. "Housed in a beautiful powder coated Blue 16ga. steel enclosure, the  dual-channel Full-Drive 2 Mosfet gives you the best of both worlds. The  first channel is the Overdrive Mode, capable of clean boost or  non-compressed overdrive or choose light to medium softer overdrives all  while retaining your guitar's original tone. The Tone knob is a very  effective presence control that can smooth out or add upper harmonics.  The second channel is the "Boost Mode" with its own separate distortion  control for medium to higher gains with a more singing violin-like  sustain."