ftpsesame helps the FTP protocol get through your pf firewall. It does
this by passively analysing FTP control connections and adding rules
into a pf anchor when an FTP data connection is about to commence.

You might want to try ftpsesame instead of ftp-proxy(8) from the OpenBSD
base system for the following reasons: 
- it runs on "transparent" (no IP address) bridges 
- you need packetfilter performance on all data connections 
- you have to handle lots of simultaneous sessions 
- you do not want to redirect any traffic to the firewall itself: for IP
  accounting or other reasons 

In general, ftpsesame is a good choice to run on a firewall in front of
multiple FTP servers, where no NAT is involved. ftp-proxy(8) is usually
the best choice when users behind NAT need to access FTP servers on the
Internet. In other situations it depends, sometimes they are useful
together.