There's a bunch of video's on YouTube with guys running these boats all over, including on lakes. One video shows a guy with 2 kids on his and they stand almost the whole time.
Interesting boats, and doing a little research on the web, they almost seem to have a cult-like following. Many guys swear by them.
I wonder if the Gheenoe is a better choice than a flat-bottom jon? Smaller jons worry me on bigger water as well, with the low sides. The Gheenoe has taller gunwales and seems maybe a better choice?