That breakout board would be fine for connecting the stepper motor itself to. It incorporates many of the features that your board already has. So, for one stepper with controller, the breakout board is not needed. If you want to remove the stepper from the board it is on, then the breakout board would be useful.
Well, assuming you have at least one other stepper to connect to it, and the stepper's voltage and current requirements are within the limits of that breakout board.
What would you keep in mind when connecting an Arduino to an external board?
Voltage and current.