The basic is actually only single zone, theres no option to have different temperatures left to right.
We have managed ok with up to six in the van in 40 degree+ in spain with just the basic aircon.
Factory tinted windows help as does the double glazing, the rear passengers don't seem to get at all hot from the sun shining through the side windows, whereas my right knee always seems to catch the sun.
I actually hate the climatronic bit, I have it on out of our other cars, & prefer the simple controls. having said that it would be nice to also have simple aircon in the back.
Until 1998 I had managed all my life without aircon in any car, the best I could hope for was a rug to sit on to temper the heat from the superheated black vinyl seats that I seemed to have in every car.