I didn't have the patience to find out how to use this. Wrote and cron'ed a script myself instead (using apt-get). Also it can't discern between the Mint "levels" of packages, so "dangerous" updates are happily applied too. Note: There's the same problem with my own script; but at least there I know what's going on.
This would be a great idea except I can't tell what level security updates it is going to install. Am I going to allow an unattended upgrade of level 5 patches (security updates or otherwise) when the Mint Update Manager identifies them as 'dangerous updates'? Yeah right, I don't think so!