There is no way to download a backup?! This is a must.
I spoke to the Managed WordPress team about this, and unfortunately with the way our free backups are stored makes making this change difficult at this time. However, we have a service called ManageWP that might be able to help with your back needs. We are also working on a premium backups feature that will be able to allow you to download your backup. Either of these options would allow you to download your backups.
I am happy to update you once the premium backups feature is available.