The Megalodon macropads use circular splined encoders, while the SENSE75 uses a D shaped encoder, so it won't work out of the box. However, the knob can be modified by drilling out the plastic insert using a 15/64" drill bit to remove the keyed part of the insert.
I just tested this and the knob looks great on the white single knob macropad. It also works to replace the small knobs on the 38% triple knob macropad and is a huge improvement IMO. These knobs are slightly larger in diameter, are a bit taller, and have knurling, making them much easier to spin easily and accurately.
Side note: These knobs will fit the GMMK Pro out of the box as it uses a D shaped encoder as well.
Yes they will, they are slightly larger in diameter and shorter than the stock knob, so there is a bit of a gap between the knob and top of the keyboard.