I dont have experience with the bris boats. At first glance they look like what you are after, a budget boat. $1000 for a new whitewater boat would have me questioning the durability, construction, etc.
1.2 mm pvc is the industry standard. The quality of said PVC and the construction are the concerns. A 5" I beam floor is a good size, as long as the I beams stay together. I assume it will be in the quality realm of the first saturns, not amazing, but they have gotten people down rivers.