If you fish with a single hand rod you will get better distance and have more options with a shooting head and mono shooting line combination.     Integrated shooting head like Airflow 40+ are Ok but only offer one sink rate which will not cover all water depths and current speeds.    Stand alone shooting heads can be changed quickly if they are attached to the mono shooting line with a loop to loop connection.     Even if you can find one a full sinking line is the worse option for a number of reasons    Nobody is using such lines anymore so stay away from them.     With a sinking shooting head you can also practice "heave and leave" fishing at the stream mouths at Lake Taupo 

A sink tip line is just another integrated sinking line but generally has a shorter sinking front portion.     All these lines will catch fish in the Tongariro but lack the flexibility to fish the range of fish holding waters of this river.     An other option with more flexibility is Skagit or Trout Spey where you can change the sinking tips.     You can use this method with a single hand or double hand rod.