I wonder how sturdy they might be? A six weight line weighs 160 grains in the first thirty feet. (with a margin for error calculated in). That weight cannot vary too awfully or one is no longer casting a six weight line.

Those ridges would seem to require that the material in the ridges be taken from some other part of the line. What are the structural trade-offs? I really don't know but that us where my line of questioning goes when I consider this point.