The first post in the forum about this plugin has confused me.
My experience over the past 6 weeks is that the plugin ONLY checks when manually invoked.
If that is correct, I would earnestly hope for a feature addition that would allow 1) the check to run when admin logs into the dashboard or 2.) (I understand that this one is asking a lot, so okay...) make it run on a cron with an e-mail alert when a plugin disappears from the directory.
For me, finding this plugin was very important because I have been burned once in the past with a plugin that was pulled from WP due to a vulnerability. But with my site very static I don't log in sometimes for a couple of months. Getting an e-mail note would be a great service. But thank you White Fir Design for creating it just as it is.