I have taught myself to use both sides.
I find it easier to use a box call by pointing the paddle or striker away from me rather than at me in my hand. That way I can cut better and can use both sides of a box call easily.

One side is deeper in tone.
Also by holding the call in my left hand, thumb on one side of the box I can move my left hand thumb up and down along the side of the box call and this helps soften the tone if I need it.

Experiment - think outside the box on uses of calls. Sometimes it works well and other times not at all.

JW

JW