Hello Auoji, mirror film always reflects equally in both directions. The side that is brighter has a mirrored effect. At night, for example, the effects of inside and outside are reversed. This is also the case with this film.
During the day, I look out and no one looks in. At night, everyone looks in and I don't look out. It only works for me on windows that are illuminated by street lighting.

So it doesn't matter which side of the film the static cling is on. It is only on one side, the second side is not static. You can apply the film to the inside or outside of the window as you wish.