They're more stable than you think. I've ridden an eboard for around 1500km this year, and although I've taken some hard crashes (always wear protection, I lost the skin on my hands once and never again) they have been down to me overestimating my grip or underestimating the obstacle. Every time I've hit a rock I've just gone over it.

A lot of it is also the different, more forward leaning, stance you assume on an eboard.