Any factory unlocked iPhone 5 board that accepts a SIM (meaning a phone unlocked for all GSM networks) should work in New Zealand for placing voice calls.
However, the 4 available iPhone 5 models [ A1428 (GSM), A1429 (GSM), A1429 (CDMA), A1442 (CDMA-China) ] differ in their cellular data network compatibility. In other words, you should get a GSM-A1429 to be fully compatible with New Zealand's data network and to support 4G.
Here's an article that explains the main differences between A1428 and A1429. You can look up more articles.
And this guide from Apple shows you the different models and their network/country compatibility.