I have downloaded the BT Cloud App to my iMac and selected one directory on my hard drive, with a few files in it. The directory and files now show within my BT Cloud. I'm quite sure that if I put the BT Cloud App on another device and log it in, the directory and files will show and I'll be able to retrieve the stored files with the directory structure intact - I've not tried it but that's accepted. As far as I'm concerned I need do nothing else on my computer other than log the App in automatically when the computer is in use, until the day when I want to retrieve something. I shall move whatever I want backing up to directories below the one I've set up in the App.
I'm aware that data in transit between the BT Cloud and my computer is encrypted. That's good.
I also have every faith that BT doesn't inspect my files for marketing or other purposes, that's not an issue.
As far as I can see there's no two-factor authentication available to confirm the BT Cloud App logging in, and I don't think that would be convenient for my needs even if it were.
I do know that antisocial people on the Internet try to discover my account details, including passwords, for my online services. They have malware which could monitor my keystrokes. One day someone will work out how to access browser remembered-passwords and then we'll all be in trouble.
Since I have a possibility of my BT Cloud account name and password being stolen due to my own carelessness, I feel I need to encrypt the filenames and file contents of everything I place on my BT Cloud storage. Then, if antisocial people on the Internet log into my BT Cloud, they will not be able to benefit from the contents. Obviously this at-rest encryption within the BT Cloud can't be a function of the BT App, otherwise the thieves will authenticate against it just by using the account name and password they stole.
Before I re-invent the wheel, anyone who's gone down this avenue might like to post about their experience.
I'm Operating System agnostic, if that helps. I run the systems I use in VirtualBox with shared virtual-network access to the hard drive backup directory, the OSX on the iMac rarely gets seen by me.