We do not recommend anyone purchasing a brake controller in New Zealand.  None are made here.   The authorized importers and their distribution chains are adding huge margins.  Most buyers do not understand the technical details,  lots of advertised products are very thin on data. 
Whatever you can find here,  easy to find cheaper in US, or if you are set on some of the low grade-yet expensive trailer mounted units, AU is still cheaper.   amazon.com is the best place for controllers if direct shipping to NZ is needed.   If you have a buddy in US that can buy local and mail to you, you can save some vs. amazon.

We sell a good quality inertial controller out of the US.