They are perfectly edible and the local NZ fish were being exported back to South Africa by the container load. I smoked and sold the stuff commercially here in NZ and my product was shipped all over both islands. The smoked product (not mine) is still sold in some shops here in NZ that sell South African produce. If prepared correctly, it can be an excellent table fish. One of the biggest problems is that the disregard that kiwis have for the fish means it isn't handled like all fish products should be.
Yes, it often has "worms" but these do not detract from the flavour. The biggest problem is mushy flesh which is not prevented by good handling. The fish go through times of the year when the flesh is useless as anything but bait or berley. The darker the flesh, the better the condition of the meat.
Excellent on the barbie basted with garlic butter or roasted in foil with garlic or lemon butter. Many a kiwi has scoffed it by the plateful in my home and refused to believe it is couta even after I show them the boxes of skin-on fillets in my freezer. If filleted correctly, there are no small bones but many long bones which are only easy to remove when the fish is cooked.
I used to catch them semi-commercially, working two 100 lb handlines simultaneously. Hard, back-breaking and possibly dangerous work if you don't know how to quickly break their necks when you swing them on board and under your armpit.