zapper vs electronic muscle stimulators

I have been researching electronic muscle stimulators, as well as those electronic face lift devices Most of the EMS can be adjusted to be used as "TENS" units - that is their pulse interferes with pain signals. The muscle stimulators & the face lift units contract the muscles, but will not bulk you up as in weight lifting.

I must say that I am rather confused, as none of them really give a lot of info.
I compare the numbers. They all use 9v batteries. ( some have ac converters)
They have variable HZ 2 to 150 or more. I see that the Clark units give "KHZ" Which is more? This is the frequency of the pulsing right?
What does the volts do? I understand that you do not feel volts.
Why is there not more info on these devices as to just exactly what is th effect of milliamps vs the microamps.

These units have variable milliamps. I would assume that 0 + mA would mean that the first "notch" above 0 would be the micro amps?
They use adhesive electrodes. The face lift devices are usually hand held and have silver electrodes.

I have also been reading about electrotherapy and electro accupuncture. It is all very interesting, but the info is EXTREMELY sketchy.

So what exactly is the difference between them and the zappers?
It would seem that the muscle stimulators would be as effective as the zappers, and some of them are cheaper.

I would appreciate hearing from anyone with info or where to find more detailed info. Tweet