Flatworm Exit does work, VERY WELL, but it's typically dosed at 3X the recommended dosage.
It's VERY IMPORTANT to remove as many flatworms, before and directly after treatment. When Flatworms die, they become toxic. For everyone you see, there's 50 more hiding, so you have A LOT more than you see. If they all die at once, in your tank, they can crash your system. So, siphon out as many as you can, before treatment and remove as many dead ones as possible, directly after treatment. Have a large water change ready to go, just in case.