The MF Flange is a 100% analog BBD based harmonic manipulator with a dedicated voicing switch and mono or stereo output capabilities.
In this video we get an overview of the features and hear the different voicing capabilities. With one voice, giving a much more vocal quality to the pedal.
The expression pedal input is assigned to the Time control. You can use an expression pedal to manually sweep through the delay frequency range of the MF Flange, but as with all the Minifooger pedals the expression input is modular friendly so your modular synth could be used to control the time.