I have no direct experience using a zapper but have heard many success stories. My approach will never include using one though. They might be extremely effective at killing some parasites, however it is completely unnatural, and I would question our bodies capability to eliminate what might be very large numbers of dead ones. If they don't get eliminated properly, the model I propose sees the ones that remain having more toxins to feed on, and they will become stronger. The toxic log jam in your lymphatic system will feed other parasites that survived.
I would say zapping is likely safer than oral capsules though. Capsules will cause systemic infestation by chasing the parasites out of your digestive system.
Whatever approach is taken, I firmly believe the cornerstone and starting point should be simple detoxification. Start there, do it for the rest of your life like everyone should anyway, and that might be all you need.