They say:

The FZ-5 is a modern pedal built for the modern guitarist, but the sounds you can get from the FZ-5 are pure retro. Looking back at the glorious rock sounds of the ’60s and ’70s, the FZ-5 recreates its vintage fuzz through BOSS state-of-the-art COSM technology. Recall the fuzz-filled flavors of classic pedals, such as the Maestro FZ-1A, Fuzz Face and Octavia pedals, and kick ’em into overdrive with the FZ-5’s Boost knob. BOSS’ proprietary COSM technology allows guitar players to recreate classic fuzz BOOST control for more aggressive tone. The FZ-5 is the perfect weapon for players wanting to beef up their rigs with classic retro fuzz artillery.