Stated plainly, so you can find out here rather than halfway through commissioning.
Passive mode only
Active mode (PORT) is not implemented. Passive is what you want from behind a home or office NAT anyway.
The address the server reports in its PASV reply is deliberately ignored in favour of the control connection's address. That avoids the common failure where a misconfigured server advertises a private IP address that the client can't reach.
FTPS data channel
Some servers require TLS session resumption between the control and data connections. That isn't exposed by the underlying framework, so if your server enforces it, transfers will fail with a handshake error.
Options: use plain FTP on a trusted network, ask the provider whether the requirement can be relaxed, or use different tooling for that server.
SFTP is not supported
SFTP runs over SSH and is a completely different protocol. BroadcastSync is FTP and FTPS only.
Symlinks are skipped
Symbolic links are skipped rather than followed, to avoid loops that would otherwise download forever.
One file at a time
Downloads run sequentially on a single connection. That's ample for typical mirroring and considerably gentler on shared hosting than parallel streams — which tend to get throttled rather than finish faster.