i have tried two different zappers and quite frankly they did not work at all. i felt VERY uncomfortable during the sessions and my body kept telling me it was wrong and to stop. i really really disliked the experience. i kept at it for a good while just to prove to myself whether or not it would work, but finally i gave it up and haven't regretted it at all.
so, i guess its different strokes for different folks. not everything works for everyone. zappers work for some, not for others. same with rife.
as for us having the essential tools inside ourselves to heal ourselves, yes i believe this absolutely. healing starts from the heart and works its way out into the body. and, as you say, truth is the ultimate healing frequency.