Actually, we are not to discuss whether frequency matters to you or me. The original question was about the difference between Beck BE and Clark zapper.
The difference is that their inventors had DIFFERENT principles of operation in their minds when they created them, it was already been said.
It is true however that to some degree both devices share the same ground cuz both do use electric current and both use the form of alternating current (there is frequency).
BTW, if you claim that frequency is ALWAYS required than you question the validity of Kaali patent, which was the beginning of Beck blood purifying work.