interesting how folks compress the piston
I just did front brakes on my son's 08 MS3.
I simply took off entire caliper, by undoing 2 17mm bolts mounting it to the hub. Pads then are right there to be pulled out.
Anyhow. On driver side piston was so much out that I could not remove caliper off the rotor. I have large C-clamp that I always use to compress pistons. Fair enough, if you have antirattle spring removed, behind it is square window showing outer brake pad clips. I simply placed C-clamp screw into the window, having opposite anvil side of it around caliper. Few turns of the screw, piston is pushed in, and voila. Thereafter, remove out pad only, screw C-clamp deeper in, until it pushes against the inner brake pad, and press piston all the way in, using old pad as pedestal. That's it. No channel locks, or any other tools needed.