The country is very easy to navigate with just paper. However if you do want a hand held device I have found the iPad to be very suitable. Connect it to the Garmin GLO remote Bluetooth GPS and you are good to go.
If you are buying a set of maps or an E map be cautious as the charts all change in November. New Zealand only updates airspace one a year and it is around November. There are some big airspace changes particularly around the Queenstown area this time around.