[dnanian]

It is sufficient, in general, as long as you can read/write the files (and the external drive has ownership turned on). But, it's not necessarily very fast, since all of the files will be copied every time.

There's no reason to erase the backup drive every time you want to backup your user files. In fact, there's no reason for most users to back up the user files separately. Just use "Backup - all files" with Smart Update. It won't erase the whole drive, it'll just update the things that are changed, user files, system files, whatever. It's not slow...