Which zapper???

The ZP unit is not an exact copy of the Clarke unit. In fact, it is not even an approximate copy. Sure, if you hook an oscilloscope up to it while it is sitting on a table, the output voltage wave form appears to be the same as a Clarke unit. But when connected to a body, particularly with very conductive contacts such as damp handles or copper footpads, the output distortion is significant, and very different from that of a traditional Clarke unit. Later-generation devices from several manufacturers tackle this output distortion with output amplifiers that are designed to drive current through a human body, as opposed to the chip used in the original Clarke unit, which was designed to drive current through a turn-signal relay in a car. Not that there's anything wrong with that.

As for "analog" vs. "digital", these concepts have no effect on the "quality" of the output of a zapper. ZP and the original Clarke circuit use two variations of the same oscillator circuit. Both are based on a resistor-capacitor timing circuit which switches between two stable states. Because the voltage across the capacitor ramps up and down, some people call this an analog design. It isn't. I know because I'm a snob. Anyway, it is semi-analog, semi-digital, and completely irrelevant.

What matters is the output circuit which supplies the current to the electrodes. The Zapper world is divided into three basic groups: 555-based (Clarke used an LM555 chip, later variations use the newer, better LC555), low-power CMOS based (ZapperPlans and others using basic CMOS logic gates for the oscillator and output circuits), and high-end (microprocessor controlled, variable output voltage, programmable frequencies, constant current outputs, etc. etc. etc. some or all of the list). Of the 3, the low-power CMOS guys have the lowest potential for performance by design. You can't beat the price, and they have a boatload of fans around here, but the circuit design is, well, low power.

ak