> The rules are all added together and applied at the same priority. Order doesn't matter.
If I make several firewalls, and the order of the rules when mixed results in unexpected traffic flows compared to the firewalls being applied individually, I have a bug that is hard to see, only experience during traffic as "timeout" or "not a timeout", and because of a lack of logging, no way to troubleshoot other than rewriting all the firewalls to try to remove any possibility of conflict, or writing whole new firewalls.
If I understood correctly, it's basically unsafe to mix more than one firewall per droplet, and in general a pain to troubleshoot. This is in contrast to iptables, where you can have multiple tables and chains, they follow a prescribed order, and you can mix and match them with expected results. Not to mention you can add logging whenever you need it.