Not Chas V’shalom to make light of a Minhag, but this particular so-called “Segula” seems to be making it’s way to the top ten.
There seems to be a Machlokes how to be Mikayem this Chiuv. Do we bury the key inside the dough? Place it next to the baked Challah? Place a key next to the Challah while it’s baking? Shape the Challah like a key? Take the key from the Aron Kodesh and poke holes in the Challah (Minhag Nadvorn)? How many keys? Use your house key? Car Key? Key from vault?
So many questions and so few answers.
The big question: How many people making Shlissel Challah are following the Minhag of their parents? Did their mothers do the same?