This plugin is great - and just "does what it says".
There a few useful options including the ability to notify users upon enrolment, and trigger the enrolment action (once added to a Course as an Enrolment method) based on various different criteria.
We actually use this plugin on our public plugins demonstration site, so you can see it in action for yourself You can experience this plugin for real as a user on: http://plugins.moodlebites.com