I’ve used it twice in two days now and it’s fun.
We have the benefit if being able to see any door-to-door people coming up the path, which gives you the seconds advantage you need. As soon as I open the door, and before they have a chance to start their “I’m not trying to sell you anything” spiel I ask “Who are you with?”.
Both have appeared a little stunned, they don’t expect a question before they can start and they abandon their script to blurt out the name of whoever is paying them a pittance.
A simple “no thanks” and walk away leaves them floundering on the doorstep before the long march to the next house.