Plone is very powerful, flexible and secure out of the box. It is relatively easy to install provided:
- You have your have a server, and not on a shared hosting. You can't just upload a bunch of files via SFTP as is common with many PHP projects. A small VPS server is fine.
- You are at least a little comfortable on the command line and with basic Apache/Nginx configuration
While out to the box Plone is very easy to get going, customizing Plone can be difficult and require much learning. A large part of the reason for this is that Plone is more geared toward sites that have 10's or 100's have active content managers with the security and workflow concerns that that entails. That said, I have deployed Plone for a number of smaller sites.
I don't know what specific tools that Flarum provides that make make it easier to integrate with other PHP based CMS systems. However just because Plone uses Python doesn't mean that you can't integrate Flarum. For example, I have integrated both Disqus (proprietary) and Discourse (based on Ruby) with Plone.
