I use the $10 zapper from zapperplans.com and it works great for me! acording to Dr. Clark: "Any positively offset [DC] frequency kills all bacteria, viruses and parasites simultaneously given sufficient voltage (5 to 10 volts), duration (seven minutes), and frequency (anything from 10 Hz to 500'000 Hz)." So, effective? I'd say acording to Dr. Clarks Book, it's effective :).