Sorry, I've been off enjoying retirement and hoping we'd get summer sometime soon up here in New England.
I tried the IDO when I was in Bonaire, and those of us who tried it agree that it is a real help with easing the effort of lifting the sail. However, we also agreed that it would be a boon for "quick and easy" lesson for resorts, but would not really help the student who really wants to learn to windsurf. It is an *aid* but it won't eliminate the need for good technique and the teaching of good technique. If the student really wants to progress, learning to uphaul easily and comfortably is a necessary technique that cannot be avoided for long. It is a very clever and excellent invention in its own right.
It may also be a bit of a negative since because the sail/rig does not fall into the water, there will always be some wind in the sail and the whole package (rig, board, novice) will keep blowing away downwind, resulting in a more arduous trip back upwind. Pretty much as noted.
In addition to the quick lesson for never-evers at resorts, etc., I can see that it would be good for handicapped folks. But you would need to keep them on a tether line or keep a very good and close eye on them and be ready to bring them back before they got too far away. A Gemini might be the solution.
The IDO was pretty funny/fun for playing around. It was like one of those knock-down punching dolls. Knock it down, and it bounced right back up at you. You could lie down on the board, and the rig would keep on sailing while you stretched out. Off the wind. You still needed to work at coming back upwind.
Overall, if it helps with the "just want to go for a ride" and marginally motivated students, or the handicapped, it is fine. But the instructor will STILL HAVE TO KEEP A CLOSE WATCH on whoever is using it. There is no substitute for learning good windsurfing technique.
I second all that Roger and Richochet have said about the IDO. As an instructor, I would prefer to ride on a board with the younger kids and the lightweight but tentative student, or use a tether such as Roger has described with the others.
I hope this helps, but please let me know if you have any questions. I will pay attention now that the novelty of freedom has worn off (just a tiny bit...).