First, quackwatch is that last place that I would consider as being open, fair, or reliable information. They are paid by pharmaceutical interests and organizations to denegrate therapies that are not profitable to the established medical profession.
There has been one study done that shows that zappers do work.
Dr. Thiel's zapper study showed that 95 percent of zapper users showed positive results.
Also, another page shows statistical data on customer success of zapper effectiveness toward the bottom of the testimonial page.
98 - 99 percent of the customers who used this particular zapper suggested that the FDA approve this device.
After all, the most reliable source of information on a product is the people who use it.