You've missed the point - because the DNS-323 is designed to be a NAS server, and not just an ftp server, connecting to the internet without a firewall is a security risk - even without the bt client running, the SMB shares are still exposed, every service running on the device is accessible to the public, not just ftp, admin web pages, AV, the whole ball of wax
I'm not going to belabor the point - I'm not the one that's exposed - if you're OK with it, fine - the reason I'm posting this is so that other users know which path to take to avoid unnecessary risk.