The do work, but not really the way they are advertised.

I found better results from using an "eggshell" acoustic foam glued onto the dynamat/road kill inside the door.

The basis of the idea is to dispel/deflect the rear-wave harmonics from re-radiating through the cone.
This can not work on less than 500Hz inside a door, and certainly not with only 3mm thick pads.
The acoustic foam is ~40mm thick, and works much better.