It's not too bad. There's only about four turnings really. It's a long drive, and you couldn't round-trip it in a day. Be careful though, I got fined for speeding on that drive for doing 111kph in a 100kph area. In the UK, the police wouldn't bother you for that small an indiscretion so I was surprised to say the least. I would guess that they target the many tourists driving the route. The trip does take in a fair few different types of environment. There's some desert like areas, some towns, you drive along at least two lakes and once you go through the tunnel you're driving in mountains, so it's quite entertaining. You can fly from Queenstown if you're in a rush, and that can be done in a day.

Yes Hertz had a sat nav available to rent, which we had. We also had our phones, but there's little service.