That's easily solved with Backblaze backing up one of the synced machines. Then it's $5/month for unlimited with off-site backup.
I agree with you that this is a very important consideration: Sync services (even Dropbox) are not backup services and shouldn't be treated like they are. You are in an even worse predicament if you are using it to sync everything locally.
I agree with you that this is a very important consideration: Sync services (even Dropbox) are not backup services and shouldn't be treated like they are. You are in an even worse predicament if you are using it to sync everything locally.