No personal experience, but we don't do many rifles that have the stock AR handguards on them when they leave the shop. Actually, I can't think of the last one we did do that kept the clamshells in place.
In any event, it would appear like a sound product, at least from application on paper, but the fact that it is made out of polymer, and not aluminum, gives me some pause....
$20 plus shipping - could be worth it to you if it works out. *shrug*