The main problem is that when you want to customize its rules, the default way to do this is to use a command-line and text based interface which means that you will have to work with the sometimes uninviting Terminal app. PF works well, but room for improvement still exists. In spite of the fact that IPFW worked brilliantly, with the release of macOS 10.7, all versions of macOS switched to the OpenBSD PF (short for Packet Filter) firewalling solution, that brings some improvements over the now outdated IPFW. A while ago macOS came with two default firewalls installed, IPFW and IPFW 2.
