Our first booking was cancelled due to weather but Minnie happily re-booked us. There was no charge for the person in our party who couldn't make it on the re-scheduled day. When we reported at the water taxi at 8.30am, there was a fairly steep access to the boat, but people to help you board (and subsequently debark on the island).
We had our own guide (Deborah) who was very knowledgeable about the history, Maori mythology, flora and fauna of the island. There was a talk for about an hour, morning tea in the lodge, a guided walk for about an hour, lunch After the home-cooked buffet style lunch with the other group who had overnighted in the lodge, we were free to do whatever we wanted - go for a walk by ourselves, climb up to a viewing point, relax in the lodge and watch the birds around there - until the boat returned to pick us up at about 2.45pm.
We saw takahe, pukeko, kaka, weka, fan tails, bellbirds, tui, kakariki, kereru, NZ robin and heard more. Disappointing not to see kiwi, but the people who had overnighted on the island had seen them.
There were some pebble paths that some people would find difficult and no wheelchair/stroller access that I saw. It would pay to discuss access with them before booking if it is an issue for anyone in your party. Bring walking shoes, sunscreen, hat, camera, water bottle - there is nothing to buy on the island.
It would be possible to get to the departure point (Coastguard Station at Paraparaumu Beach) by public transport on the day from Wellington - train then bus - but would mean a very early start. There is a Hostelling International hostel and a couple of motels less than 5 minutes' walk away.
All in all, it was a great experience and highly recommended.