If the ZBE head provides a steady light output, it does so at the expense of maximum light intensity.
It produces whatever light output the controller demands of it. If it be the max then it is the max...
One tube is always at maximum intensity and the other tube is turned down to adjust the contrast. It is the same with every other head. If it is a fixed illumination (undimmable) head then the timing of one of the tubes is reduced in relation to the other. The effect in printing speed is the same.
The ZBE gives the option(s) for various control strategies where contrast can be changed but printing time is kept the same - in this case the lower contrast settings do cut down the light. The same happens with regular VC gel filters without much complaint. The ZBE also has the option of keeping the printing times at their shortest and automatically adjusting the printing time as contrast is varied. And programming this function for the responsivity of various papers. And programming the blue/green balance for various grades for various papers so the same dial setting produces the same contrast on all papers. And scanning the image on the easel and for the selected paper and automatically selecting the best grade and exposure for the image. And, and, and. To compare this with an Aristo ...
Compensating timers/light integrators work mostly, and mostly they work well enough. But so will a plain Aristo if you keep careful watch over heating time and printing duty cycle. Problems with VC cold light heads arise as the lamps age. The differential in light output changes and unless the integrator has a sensor for each lamp the integrator will lead one down the garden path. And individual lamp sensors won't detect the change in the lamps spectra as the lamp ages, for that one needs filters matched to the sensitivity curve of the emulsions or an integrating spectrophotometer.
Whether the features and precision of the ZBE is of use is something everyone has to judge for themselves - as the story goes Edward Weston produced prints with a peice of glass and some sunlight for printing and a raincoat thrown over a card table for a darkroom. The equipment is not the limiting factor.
It seems the owner will be happier with something simpler. But sell the head on to someone who will appreciate it and be willing to keep it running.