I totally agree with @IIIM5 about TZ & rear AC vents. I own Prado 96 TZ 1KZ-TE and Dual AC was my top priority when looking to buy one. There is a reason... they put vents for 2nd and 3rd rows.
My experience... Prado parked under the sun for hours and at around 37*C, with dual AC it just takes minutes to get the entire cabin pleasantly cooled. Without dual AC, you would need to put AC on full blast but folks in 3rd row will still be sweating.
Dual AC just requires more coolant in radiator... I thinks its 9 liters for dual ac and 8 liters for without. No difference in power or economy.