We setup vsftp on an Ubuntu server for our customers. We had a few customers ask for a secure option, so we setup explicit FTP over TLS and we removed the ability to connect unsecured. Now we are having customers ask how they can connect using the Windows command line FTP client, for which they have already created automated scripts around. Is it possible to use the Windows command line FTP client to connect to an FTP server that requires explicit TLS? We have searched the web and it seems that the solution is to use another client, such as FileZilla, but some of our customers do not want to use another client. We also do not want to force them to use another client. Maybe TLS isn't the best option for secure FTP?
It is not.
A far better solution is to use SFTP (SSH File Transfer); it can use public keys to authenticate (which is ideal for scripting) and is supported by virtually every client out there - except, obviously, the standard (and worthless) Windows one.
One of the better ones is WinSCP.
The only time that I would recommend FTPS is if you're running it on a Windows server where there is no native SSH implementation. Since you're running Ubuntu on the server, you should look at SFTP/SCP for file transfers. There's no native tool for Windows, but FileZilla, WinSCP and many others support both GUI and command-line scriptable transfers.