From watching the video of one it doesn't look like there is a lot of directional control or stability with those tubes. When the bottom of the tube hits the water it bounces in unpredictable directions. Combine the high rate of speed with a novice rider and I can see how you would have a lot of accidents. I don't blame the COE. Death on the lake with an approved COE device doesn't look good on the front page of the news.
pk

They've already been withdrawn from the market. A neat idea that wasn't very well thought through. Saw one this summer on the intercoastal waterway near Wrightsville Beach.