I've found that by adding this plugin to a course, I can add participants who are not enrolled in this course.
Is there any way to restrict participants to the scope of the course?
We have used F2F for a while and have found the following issue.
If you enrol students into your course via F2F they usually go in this "No role".
This results in students not being able to participate in activities.
Not sure about "restrict participants to the scope of the course"... once enrolled they see the course unless activity "restrict access" settings are in place.