I used to use those darn things on my BDS and BP is correct...they get bad real fast. Excuse my ignorance (my drum is on a Fed-ex truck right now) but doesn't the air dampers included in the kit do the same thing??
You can buy this stuff fairly cheap and cut it to size. It's black so nothing to show it's getting hammered like a fridge magnet would. Amazon sells it also. I bought some when I was planning to drill large holes up near the top of my drum for hanging meat.