Fellow Kiwi here.
I've seen these things in The Warehouse as well, and wouldn't go for them.
If you want WFO like performance, but don't want to spend a lot of money, Jeff (Shuboyje) said in another topic/post:
"In your situation I would probably build a quality base(like they describe in the Pompeii plans) (in your case make it portable), insulate it well with board or vermicrete, put a firebrick floor on it, and then build a cob oven. It is easy and cheap, but functional. If the bug bites you and you think it will be worth your time and money to built a true masonry oven you simple demolish the cob dome and build a masonry dome on top of the stand, insulation, and oven floor you already have."
I think that is excellent advice.