They look unlikely to be correct. I suspect the naming might be attractive, but please look at documentation.
Local folder or drive describes their format and use for that case, but forcing them to FTP usage is unusual.
Windows Drive Letters describes cases they intend to solve. FTP fits neither. I don’t know what result will be.
What I can say definitely is that if the intent is to have one job on two drives, it won’t work, as there is heavy reliance on knowing destination content, and switching drives breaks that. A job for each drive should work. Exporting and importing can move the configuration, then you can adjust things like folder for second drive. Using a different folder on each drive is probably good because you’ll get an error instead of a wrong write, however please test a wrong-drive use on an unimportant backup. If it’s too ugly there may be another way.
Backing up to multiple USB or external drives? has further explanation about what you might be trying to do.