As you say from the start, I have a real problem with overflights by helicopter for tourists. I can not say that my carbon footprint for the year is very good, given the many planes I take, but I still try to promote non-polluting activities. So when I was asked to fly over the island of Reunion in a helicopter, I really had a case of conscience ... I ended up trying, for the experience, and because everyone seems to think Reunion see that from the air is essential. And, ultimately, it is not wrong: it is fully realized very special reliefs of the island, with its circuses, plains, beaches.
However, I would recommend the ULM at the expense of the helicopter, and it has nothing to do with my conscience full of pollution. No, I recommend ULM because between my experience and the stories of helicopter ULM buddies, I'm jealous of not having been in their shoes!
There are several companies that offer helicopter flights and roughly two models of vehicles. In the one I took, were shipped to six: two rode front next to the pilot, and four were piled behind. Except that you do not know in advance what role you will be assigned all depends on your body (they balance the weight) and the base of the other tourists. It may be that you spend the entire flight on the two back seats, and it's close to 300 € per hour per person. Personally, I have been lucky in getting the window next to the front, although I think that the best places are in fact those from behind the windows are opened more widely. On the other helicopter model, the windows do not open up simply: it will integrate the reflections in the pictures!
Both tourists placed in the middle did not seem disappointed, but I know that personally, I would have been wrong to pay so much to go flying with my camera on my lap, trying to see the scenery between the heads of the neighbors, as in a crowded cinema.
Besides that, microlight, not only is it less expensive (expect an average of 150 € for the classic tour with circuses and the volcano), but in addition, you are alone with the driver, which allows for a real exchange (by helicopter, he will recite a text you will understand more or less depending on the quality of your headset) and a much more flexible way. You will be next to him or behind him, and depending on the company and the weather, you will be in a closed model (ULM 3 axes, which looks like a small plane but which easily opens doors) or in any version open (ultralight, one with a kind of triangular sail, which is controlled with a bar). In all cases, you can much more easily brush the ground, whether it's approaching a crater or go fly whales (yeah, I drool!).
For overflights ULM, you can read the experience of Julian, find advice from Julie and of course through the list of providers on the website of the Tourist Office.
Whether you choose the helicopter or microlight, the price goes up to threefold depending on the chosen route. The price can go up fast enough. I urge you to see at least one of the circuses and the Piton de la Fournaise.