Not sure what the situation is in NZ, the knife you shown is classified as a bayonet, should not be problem for Australia. Mind you, if in Australia you might encounter a Border Force inspector doing those X-Ray inspections of incoming parcels who does not know what's approved.Australian here: Double edges are the real barrier to import and the swedge on this could be the killer.
From the NZ customs site:
"Any knife, with the exception of a folding pocket knife with a blade less than 10 cm in length, that —
I'd say this falls into that category and wouldn't risk it.
- is designed for ease of concealment on the person; or
- has a double-edged blade that is designed or suitable for stabbing or throwing (as opposed to cutting);"