Things must have changed. You used to be only able to pay with APD on NZ metal and some qualifying partner flights such as CX to HKG and UA to SFO.
Just did a dummy booking and now it seems that anything for sale on the NZ site is eligible to pay with APD even on non-Star flights such as Air Calin, or mixed intinerary including flights on BA. Basically you can now use APD like cash.
It's an improvement but I worry this will be a further departure from a traditional FFP that allows members to redeem X, I booking classes where the real values are.