I think the kuiu was among the worst packs I’ve had with a heavy load. I hated it, and tore it up pretty quickAlso have both. Have only hauled meat in the Kuiu and I found it pretty uncomfortable. I’m hoping the K3 is better. It seems much more comfortable to me just in general use. The Kuiu bags have nice organization but the hip belt on the K3 fits me way better. I think like any pack, each will fit you differently and one will be more comfortable than the other with no telling which it’ll be until you try them.
The buckle?I can't speak to the kuiu but I have broken my k3 twice on hunts. I broke the hip belt twice leaving me with Terrible pack outs.