They have been discussed on SSW, if the ones you saw were Sullivan "Tuff-Strand" the consensus is not good. I have tried them and they are a poor subsitute for steel cables. They are a lot bigger in cross section ( kind of flat also) and result in high drag,line bow, and reduced control feel. On the plus side they make excellent non-metallic binding material for sewing landing gear wire to plywood mounts, or would make a good stooge release line.