The Cunningham article outlines floats that have a rectangular cross section. There is a table in the article that shows width vs weight.

Seaplane's floats have a v-bottom/tapered sides That makes the planing area wider and floatation closer to the bottom. So for a given size, they float higher and plane more easily. The slight V-Bottom adds stability and serves to cushion the plane in choppy water. The general consensus is that V-bottoms don't skip as much when landing.

I make my own floats. They look almost like Seaplane's. For the time I spend making a set of floats, and considering what Seaplane charges, Seaplane would make a lot more money working at McDonalds for minimum wage. I'm glad he does it. Foam floats are superior to other constructions, and there are precious few vendors offering them any more. I believe his are the best design offered.