Questions about Monzana 3x Draft stopper

I bought them because of that and I think so. Not extreme, of course, but the noise certainly gets through a little less, I have the feeling.

there are 3 included

No, unfortunately not. You have to slide it under the door and it is fixed like this, i.e. when you open and close the door, it slides along. With a sliding door, it would "fall out".