The best way to use this is to Define users by IP.

Security is best by IP address so that it is specific.

You can assign by user ID which is cool but if someone knows the user ID then not so good.

Groups are good if you have a strict compliance to user groups in that you only have assigned admins/supers assigned to them.

For your best security with this extension, we recommend that when not in use that you disable this plugin for extra measures.

This IS an awesome Plugin for what it does if you have a site where users/subscribers are having troubles on the frontend and seeing things you cannot or if they cannot get access for whatever reason to the downloads... etc... etc.... Used quite a few times.  This is why I wrote it.