I dont know why but in all my guys on fable TLC and just Fable i never try to get the keys... i just dont think it's worth all that time getting them... is there anything REALLY worth it in those key chests?
I mean after you beat the game and play afterwords you usually have a legendary weapon so your unbeatable... and that one axe ragnarok or something found in the demon door in grey house is a pretty strong weapon i used it until i got avo's tear...
If your hero's strong enough it doesn't matter what weapon you use... (except for stick

)