Ido for little kids
Our Club, the Montreal windsurfing Association has a tandem Gemini and an Ido. We found that for very young or very litle kids that gets blown away in 5 knots gust...the iDo in front of the Gemini with a teacher in the back will help them understand better how to manipulate the sail and where to place their feet.
After a few sessions of 30 minutes on the gemini and iDO, they were ready to go on their own on a Go or START and a small sail.
And I would add that we used it as well for a humane factor on some occasions, as the iDO keeps the small sail up by itself, we managed to bring on the water some kids that due to their physical health ( cancer ) would have never held a wishbone in their live.
But yes Roger, you are right, you CAN NOT let a beginner loose with a iDO if the wind is slighly offshore. Those kids can go a LONGGGG way before they realise their is a problem. Actually, the few ones we had to chase down the lake had never realised they were gone that far , they were simply convinced they were very good windsurfers :-)