Apart from the obvious marketing gimmick, I'm not sure whether it actually offers anything for the consumers...

The T&Cs say it's up to NZ to verify the claim, they won't accept any evidence you provide. If you submit a claim and they can't get to it the next day, cheap fares don't stay around long. If they're sold through 'proper' booking engines, availability will be very limited. By the time Air NZ get to your claim, that fare may not be around. There's no promise on when Air NZ will work on your claim.

The cheaper fare can only come from a web site, not other channels, how many other web sites in NZ sell Air NZ fares? In fact, how many NZ sites sell airfares? Not many.

This offer only applies to one-way NZ fares, you can't claim if you find a cheaper QF, Virgin or whoever fare... Also with international fares, I suggest not many buy them on a one-way basis... This deal is only good for one-way, not return fares.

Also, how does joe-public figure out whether the cheaper fare is a consolidator fare? A lot of engines have trouble telling the user the fare class already. This deal also excludes any sales from other retailers.

The list goes on... Unfortunately, I see a lot of room for Air NZ to wiggle out of this.