I don't understand why this plugin does not have a 5-star rating, most likely due to people not being able to use selectors properly.
Plugin works amazingly, everything is thought of and very well done. Found it because we were going to develop something similar, but there is no way of beating what's here - excellent work.
As far as the unexpected output on activation - it doesn't inhibit the general functionality of the plugin (at least not in my testing) the error is only on activation. The plugin does go active, and it adds an option page under "Settings", shortcodes work as expected.
If the activation error keeps you up at night, here's how to remove it: http://screencast.com/t/Xvin1XGotJ