there is probably no better method than the shutdown that was designed by the operating system manufacturer.
But if you insist, uninstall the application that you have installed, shut off the anti virus and firewall, re-install your shutdown application, restart the computer, turn the anti virus and firewall back on. That will usually do it.
But you have to keep in mind that there is no assurance that third party software is going to run correctly, especially when it's not signed by the operating system manufacturer, especially when the manufacturer is updating the operating system to keep non- OEM devices from controlling it.