The problem is not in the products or the companies that make these silicon sealers. It is the restoration companies that market these products. They act as if this is the end all to your deck maintenance solution and it is far from it.
I carry a version of these products because in some instances it will have a purpose. By no means will I ever market it as the only thing you will need to do. If you want the wood to look good then you will need to do regular maintenance. Clean dirt and grime and apply a tinted stain/sealer to prevent graying.
