I have one (I should say many (:-)…
These 6 fixed frequencies are very popular ones. The sweep (33 different frequencies) around 2.5kHz is a very interesting one I have used very often.
See this page for information about sweep frequencies. http://www.zapperwise.com/e_frequency_sweep.html
This zapper is built on the MZ3b PCB and is driven by a powerful micro-controller.
A nice, unique zapper.