Findings
The using client should check that the plugin will work as expected on their hosting platform and setup, for example the mail sending functionalities.
Reason for the 'Use with caution' result
The plugin has been given this recommendation at the tester's discretion:
This is very large codebase (335124 lines of PHP) including libraries which is difficult to fully review. It has been given a short, targeted inspection. No issues were found from this.
The plugin is difficult to fully test without deploy to a production website, as, for example, the mail sending feature is linked to the website domain.