This is an input impedance control. Why? Germanium fuzz pedals generally sound bad when placed after another device. The "impede" mini-knob helps fix that. It also decreases gain.
Both are based on Tone Bender circuits. The legendary MKII has tons of fuzz with infinite sustain. The less famous MK1.5 has one less transistor for less fuzz.
The Tone Bender circuit doesn't adapt well to a tone knob. This switch swaps out capacitors in order to get three different voicings while preserving the stock circuit.
The bias sets the operating voltage of a transistor. It can change based on temperature; this mini-knob make it easy to adjust. Tone-wise, it can go from a sputtering mess to a proper fuzz.