My long-legged older daughter can handroll her Remix47, but prefers her sister's Fun 1.5 for river running.
I figured the "kids' creek boat design" of the Remix47 would be better in moving water...but all our kids have preferred flat-bottomed playboats. Talking Class II and easy Class III water. Nothing confused or chaotic, just straight up wavetrains. The hull follows the surface of the water, and they're OK with it.
Pretty interesting perspective on initial vs. secondary stability--I can't explain it to her.
Also based on what we've seen from the kiddos, the Fuse35 and Shooting Star are a bit more forgiving than the Fun. No explanations from them, just based on watching them paddle and telling us what they like.