I’ll give an EE’s perspective from the RC properties from my experiences since 1975.
Zeners always have an exponentially continuous reducing resistance above knee voltage threshold that flattens to a fixed bulk electrode size dependent resistance as in all common diodes . ON semi quotes threshold resistance as Zzt and “on” knee resistance as Zzk which is inversely proportional to the power rating (size). The capacitance of diodes also increases with conductivity such that the conductive rise time is large relative to tunnelling effects.
Tunnelling effect diodes is similar to dielectric breakdown with negative incremental resistance after the triggering of conduction, whereby the dielectric capacitance is very small just before conduction and resistance quite high.
Although unlike the RdsOn FETs where the Rs drops as the C rises during the Vg(th) transition both inversely very rapidly as the conduction gap closes, tunnelling does not rise in capacitance as fast so the transition appears as an incremental negative resistance near zero time (almost) It is so tiny that extremely fast DSO’s may be needed to capture it.
The tunnelling effect of an ESD arc to metal with <100 pF with _ kV charge voltage has been captured in less than 10 ps, and Tunnelling type diodes found to approach this depend greatly on doping and geometry yet often cannot.