I checked that out once but the safing/SPN thing spooked me. It doesn't really explain what it is and why it is needed for a software firewall. As far as I can tell is it a peer-to-peer VPN network? I don't want that. If you have a good answer I'd love to learn it.

CTO of Safing here. I hope I can bring some clarity into this.

Portmaster is actually a privacy suite consisting of many features and modules. It is often described as an "application firewall" to give people a quick, but incomplete idea of what it is.

The SPN is one of these features. It is a blend of VPN and Tor - oversimplified - and is fully optional. In fact, it is a paid feature and won't activate without logging in with an eligible account.

I humbly suggest that you add an entry in your FAQ regarding this question. I tried (quickly) to find answers in the documentation and then moved on when I couldn't find one. Take of that what you will.