You have to do this trip.
We chose Rainbow because they don't cancel flights for underselling, and they have a great reputation. We did the "Doors Off". It was a blast. The flight covered most of the island, and gave us a completely different view, of course, than the drive we did a few days later.
The pilot provided some great stories about the island, and was able to answer a wide variety of questions. He also regularly banked and rotated the helicopter when near particularly interesting viewpoints off to one side, so that both sides got a good view.
Some things to note:
They state you need a sweat shirt or similar for doors off. You do. It's not the temperature so much as the wind. A thick denim shirt was fine.
In our case, the other party chose "doors on". So their half had the door shut. Only the back half of the helicopter can be doors-off. But that's clearly the better way to go.
You will be waiting. Your required check-in is an hour before you take off. Five minutes of that is for the safety video. So be prepared for that.