We had a really great time staying in the airstream. We really appreciated David and his families efforts. (E.g. lending us children books for our daughter and giving us lots of tips for what to see during our visit.) David was also unusually responsive and helpful whenever we needed something.
The Airstream was practically new, super clean, and very fun to stay in. E.g. it has a nice stove (we cooked full meals regularly), fridge, built in bluetooth sound system, TV, USB plugs everywhere, a surprisingly large amount of storage space and many other little conveniences. It worked especially well for us as we all had roughly the same sleeping schedule.
The location in Wellington is great in that we were in the center of town in 5min by car and even on foot a few times. The immediate area around the caravan is alright. It stands at the edge of a (pretty quiet) parking lot but it does face a very small green area. The only real downside is that the motor way which is about 20m away from the side of the caravan. In the end it didn't really bother us as one hardly hears it inside but it did mean we didn't really spend any time outside the caravan in the green area.
All in all, we absolutely felt it was worth what we paid to stay there and we really liked David and his family.