While there are many tools out there for managing firewalls, not all small companies have the resources of larger companies. Well load out and capable GUIs can make a huge difference in assisting those that don't manage backend servers for a living. When dealing with firewalls it is even more scary.
I like what DO has done with simplify firewall management but do feel that the ability to allow/deny by interface is a crucial piece of the equation, especially with the advantages using internal private IP offers.
I'd like to suggest idea of adding ability to specify 'from interface' to cloud firewall.