1b - that tool is OK & it doesn't cost much. But honestly, you don't need it.
The face of the piston has grooves. I use either a huge screwdriver or else something like a putty knife to turn the piston. As you turn it, pay attention to the rubber seal around the piston. Make sure it slides & doesn't wrinkle & tear.
Depending on the rotor thickness, you may not want to twist the piston all the way in. Just enough so you can install the new pads. Then the handbrake auto-adjuster doesn't have so far to go...