That's neither good nor evil.
What matters is how you use that invisible tank once you've got it. If you use it to conquer California, that's bad. If you use it to kill Saddam Hussein, Kim Il Jung, or Paris Hilton, that's good.
They're already invisible. There could be a hidden camera in your bathroom this very moment. Unless you're stockpiling AK-47's and rocket launchers in your basement and plotting to conquer the city, I can't see (har har) why anybody would send an invisible tank your way.