Okay, I see the video confused you, but better here than after you have installed it.
What you heard Martin was a portion of my disc that was uneven on the side of the stainless pistion installed. It has nothing to do with the piston its self.
this means that you should have 4" leftover on each rim if applied correctly. These are not radius form cut. It's a simple straight strip.
yes it is normal.
What we are looking for at the video apart from a loud shhushing that you may have with yours, is the wheel would stop spinning abruptly due to the pressure the caliper maintains on your disc.
As you saw both sides turned freely and evenly. Turn your wheel on a car or motorcycle. If you put your ear as close as my phone was, you will hear that sound.