Here is my personal testimony, from my experiences.
= Conditions of Use: tested frequencies: 15Hz, 1kHz, 2kHz, 2.5kHz, 5kHz, 30kHz, 32kHz.
= Power supply : 3 to 15V.
= Sequences: 7-20; 28-20, continuous zapping, from 20mn to 8h .

First time use :
= Mild fatigue the next day (want to do nothing);
= Lightweight tingling at contact area with handles, disappeared with time.
= Slight itching when the handles are placed under the armpits or stuck in socks, for periods exceeding 2h.
= Flatulence for a few days.

Thereafter :
= Sleep comes faster and is more relaxing (often, not always)
= Ideas clearer, feeling alert (often)
= Pain throat well established (2 times), disappeared in 24 hours.
= Sinusitis (many) vanished in a few hours.
= Teeth pain with gum inflammation : Inflammation and acute pain gone after 1st session.  Remaining pain gone after 2nd session.  No other problem in this area after  several months.
= Several supposed flu or cold (where treated at their beginning) disappear within an application.
= Severe and/or sudden "depression" (3 times) gone after 2h sessions (astonishing in my case, it usually takes 3 to 5 days of hard work by other ways) 

Personal and final comment :
= So far, no side effects other than minor inconvenience detoxification, has been noted and reported on my side.

= A funny comment that comes up time to time is the vanishing of many old health problems having nothing to do with the initial purpose of buying the zapper, and a nice surplus of energy available (highly subjective, I agree).

Antonio Gomez, curious user of zappers

Zapperwise sum-up
Personal use and comments

Comments:
= I did not notice any difference in the effect of frequencies between 1kHz and 32kHz, being in (relative) good health.
= I noticed a positive difference (subjective) in these frequencies when a very low frequency (15Hz) is added (use of M.Zap2 M.Zap3)
= I mainly use 30kHz and/or FV frequencies at the beginning of use (Get rid of whatever "negative" is happening), and switch to 5kHz frequency to stay in the comfort zone.
= I place the (+) handle close to the area being treated.
= Without any reasonable... reason, my preferred program is 28-20 at 30kHz or FV (M.Zap2 and M.Zap3).
= For general zapping, the voltage can be quite low (less than 3V) and still be effective (medium).
= Having a constant power supply of 10 to 15V does a more predictable result and removes the usual questioning "is strong enough"?
= In my tests with "high current zappers" of the kind "exit doesn't distort", (internal dynamic resistance near 0 ohm), the effect of "tickle" due to the surplus of current becomes unpleasant and I have tendency to discard them after a short periods of time.  On the short term, they are more efficient.
= Tests with an antenna are promising.
= When I zap on the head (Pain inside ears, for example), I place the (+) handle at the top of the treatment area, and (-) handle in hand or under the armpit on the same side, with no-salt moistened paper towels (3 to 4 wraps, to decrease the current).
= I remain cautious in head area, where I feel the 1kohm internal resistance of the zapper too low.
= My zapper follows me throughout my travels, as an all around emergency kit.

Personal question to all: Someone has used a zapper to purify water? What were your results?

Actual trends consists in using lower frequencies, based on "the skin effect", trying to demonstrate that the penetration of the frequencies would be better with lower frequencies. 

We did not perceive any difference during our experiments and we do not subscribe to this theory.
30kHz is an excellent frequency for a general use of the zapper.

2.5kHz remains acceptable, but its 3.5 times “higher penetration" has to be proved. 

Note about 15Hz :  This frequency is part of the “natural waves” of the brain.  Classified in between Alpha (relaxing) and Beta (stimulating) fields, it is easily recognized by the brain and communicates a feeling of “stimulating relaxation”. 

The current tendency also consists in using increasingly long and repeated sessions.

The longer time recommended is done by Don Croft and its "Terminator", very unusual zapper, using 15Hz, really apart from the traditional paths, which can run 24h and more...

We see two explanations to this tendency in duration :

The action of the electrical current on the human body depends on the quantity of electricity, which depends on the current which circulates, and time
Quantity = Current x Time 

This  tendency makes then sense, because if the current (pushed by voltage) must be limited to a safety factor, only time can be increased.

This tendency can be also explained by the difficulty of the zapper to reach certain hollow organs quite well protected from the passage of the current.  When the big part of elimination has been done on the “outside”, a longer and repeated use will end up having an effect on the “inside” of these zones (and our immune system, less busy by emergencies, will be able to do a much better work, especially in these organs).

In practice, lower frequency means lower current, means longer time for the same effect
Quantity/effect = Current x Time
Current = (2Pi.Freq.Body capacitance) . Voltage

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