Yes, but in order to add new items to each piece of hardware you have to be physically co-located with all the pieces of hardware you want to use as your backup

Yes, but in order to add new items to each piece of hardware you have to be physically co-located with all the pieces of hardware you want to use as your backups. Which means they cannot be geographically distributed (or if they are that there is a period of time in which you aren't fully backed up). Which means you're either in a place where you can loose all your keys (e. g. a house fire or a flood) or your in a place where you can loose all the devices that have a key.