Like you, I haven't used the Agnitum Outpost but that's because I haven't needed to. Others such as ZoneAlarm work fine for me. Rule-based systems allow you to configure trusted ports where you will allow traffic for specific programs. In most cases, they set up "rules" before using the system. Program/permission based systems allow you to configure access for trusted programs through the firewall. In essence, they're doing similar tasks, but in a slightly diffferent graphic user interface.

Read the reviews. Although not bad, Outpost is not always one of the favorites.:

PC Personal Firewalls 2004,
http://www.transceiver.co.uk/txt/pf04.html#pfp5

Personal Firewall Reviews
http://www.firewallguide.com/software.htm#More

Outpost Firewall Pro ... Version: 2.1
http://castlecops.com/reviews-191.html

Hope this helps.

Grif