Ebike 24v relay board - switch?
I think it's a 3 wire throttle controller

This board might already consider variable speeds.
As for having multiple relays, maybe it has some relay logic going on which creates a stepped output to the motor based on the wire's inputs.
You might be able to give a straight signal to the 24V circuit if you want to use a switch, but if you want variable acceleration, I would recommend buying a throttle control.
Image credits: https://support.electricscooterparts.com/support/discussions/topics/1000083529