25kohm potentiometer is used inside the volume pedal (same with your guitar volume knob), 25k is usually used for active pickups (AKA low impedance signal), 250k/500khohm is used for passive pickups (high impedance).
when you use a booster or use it as a buffer (making the high impedance signal low impedance), you need to use in theory a 25kohm potentiometer (since you now have a low impedance signal), i was just making sure that's the case.