The Flatiron Fuzz is Electro Harmonix's ode to one of the other icons of late '70s op-amp driven, hard-clipping distortion/fuzz tones, the venerable ProCo RAT2, but with some simple tweaks to make it more usable with modern rigs, like true-bypass switching and a standard 9V DC power jack.  The Flatiron Fuzz runs the gamut from low to mid gain overdrive and distortion settings all the way up to full on, roaring chainsaw style fuzzy gain sounds with a distinctive midrange signature that is unique to the Rat style circuit.  The Tone control on the Flatiron Fuzz is actually a low pass filter with sweepable cutoff frequency, allowing you to very precisely dial in the balance of low end to high end for your guitar signal.  The Flatiron cleans up with your volume knob much better than similarly styled gain pedals, and is sure to add some unique and classic distortion tones to your rig.