I purchased a soot eater this year for my light duty corrugated chimney liner. Unfortunately I had not realized there are two kinds. One for a liner (grey flex rods more flexible) and one for fixed open chimneys (black flex rods less flexible) I purchased the open chimney version. Will this work on my straight run from the roof down, or will I need to purchase the other version? Has anyone used black rodded version on a flex liner?