I haven't seen the weta fly before - sounds like an imitation of a large terrestrial insect we have here. A fly the same size as the real thing would be big (3 - 4 inches) and hard to cast in a wind. Big trout would eat them. Maybe ask at local angling clubs.
IMPORTANT MESSAGE: please note NZ now has the highly invasive weed "didymo" in 23 South Island rivers. North Island so far is without it. One drop of water is all it takes to spread it. It is vital that any visitors clean and dry all tackle and boots before going from one river to another, or use different tackle for each watershed fished.
Fish & Game NZ website has details of how to clean gear, and horrific photos of what happens if you don't.
Tourist anglers should also clean their tackle rigorously before leaving NZ, to avoid risk of taking the weed back to their own countries. Tell your friends about this issue; if you want to help us keep the good fishing, the big message is "Check; clean and dry".
