I have one too, they're fantastic fun /forums/images/graemlins/laugh.gif: And they are really stable too due to the huge wings either side. I've not been as high as in the video yet but am getting there /forums/images/graemlins/tongue.gif
It's all down to the throttle anyway, as soon as you see the manta veering off to the side you just throttle back gently and it''l go down nice and gently and even if one wing touches first, it'll soon right itself.
Maybe the inventor is the same who gave birth to the famous air chair...
But if not, I wonder who of them used more hallucinogens when they were on the drawing board!