A little more for trick or treaters to know your house is definitely in the Halloween mood!
The knocker itself is functional, although the swinging piece will barely make any noise banging on the door so I'd recommend adding something to the  ring, like nuts, curtain rod stopper or maybe something plastic or rubber.
Double sided tape should be used for easy applying and removing the knocker on a door or wall. I've made the model to be printed out vertically as the details look better when the line is oriented that way, although laying it on the back side might be faster and less supports will be needed.