Framewise a good 8/9 but obviously there is a skin on top but it was pretty taught. It all felt pretty solid, the guy there mentioned (jokingly) about storing the Alu frame in the cold and the skin in the warmth and also banging on it with a rubber mallet. I'd have no hesitation about flat water paddling in them, I think they'd be as good as a 'normal' boat, less sure about a river..... You'd need wellies for beaching etc.
Just realized where you are, I'd really recommend you go and see one (and take your credit card...)
Cheers,
Alan