If they doubt your claim you may still have to pay the duty upfront but it'll be refunded upon departure if you follow their procedure. Very rarely a problem for such a low value item

I used to carry large, expensive test equipment in and out of NZ and you always had to tell NZ customs that I WANTED them to view the gear and sign the carnet, otherwise they weren't bothered. Certainly for a Nano or EW logger, just keep it in your hand-luggage and tell them what it is when it shows up on the X-ray. You won't have a problem.

What NZ does care about is anything that could introduce unwanted insects or pathogens into the local agricultural industries, so declare ANYTHING that could be viewed as food or plant matter, and give any camping gear (including your hiking boots) a darn good clean before you pack them. They used to clean your boots for free at the airport but now they charge for it.

Oh, and don't bring any class-A drugs or large quantities of pseudo-ephedrine either. We're really just a bunch of killjoys down here.

DH