The circuit in these modules is particularly stupid. See this answer.
Note also that the LM393 is open-drain and the pullup is through an LED so that will only get pulled up to 3V-4V. Use a resistor to the supply to get it to pull up higher.
The sensor itself is a mechanical contact that opens so the 'sensitivity' adjust is doing very little except interacting with parasitic capacitance. The sensor 'datasheet' contains a reference circuit that makes more sense:
However note that neither of these circuits really adjust the sensitivity of the sensor, more like the minimum duration of acceleration that exceeds the threshold set by the mechanical sensor.
If you did have something with a genuine sensitivity adjust you'd likely need something like a shaker table to create a consistent level of vibration. I use a small unit (ET-126 from Labworks) driven by a power amplifier for this purpose.