I tried that a few years ago. Bought 3, 1 lived. It was a Flatworm eating Machine! Like a Vacuum Cleaner. BUT, if it gets rid of all the flatworms, it will die because that's all it eats. Mine accidentally got sucked up during a water change and never finished the job.
Do yourself a favor and use Flatworm Exit. Works just as good and much faster. Follow the directions to the T!