Last I knew XF ceased allowing PHP files to be called directly from templates (think it stopped in the 1.2 version).
Calling PHP is best done via the official process of an add-on or call-backs.
This sorta explains how/why.
It would be awesome to be able to call a php file directly from a template without the need for an Addon and hook. For example:
xenforo.com
And I've got a sneaking suspicion this "firewall" is going to cause some issues with your XF site.
Much of what it touts can already be done by a well configured copy of CSF at a stack level lower than after the HTTP server processes the requests, and there are already affective add-ons available for XF that provide as good (if not better) spam protection.
I could see using it on a WordPress site or similar, and actually I'm pretty sure that is more what it targets than a forum script. It has a known issue with phpBB... and I seriously doubt it has been very well tested with XF as in over a decade this is the first reference to it I've ever seen.
And when I read these full instructions on their support for install it indicates to me that it's more along the lines of a WordPress targeted add-on.
Guess what... that means editing the actual PHP files themselves and adding it - and
src/config.php
would not be "the file". So you would have to be editing the index.php or similar actual physical
PHP
file that is called upon every page load. So, for me that would be a BIG no thank you... as every upgrade you would lose it, every file check you would be shown that a file doesn't match.
Their reference to database config/connection file smells suspiciously of WordPress.
You might want to see if a developer would take on integration of this into a simple add-on.