I have also used quite a few FC lines out there and I have to say that I have had nothing but bad luck with most of them. I lost several fish on Vanish, it just seemed to break for no good reason. The Stren is better but also seems to break for no good reason, at least in my experience with it. I tried a Japanese made FC called SightFree Aeroflo. In my opinion it is the real deal. I have had great success with it. As far as the invisibility with FC lines are concerned we used an underwater camera and filmed some different sze FC leaders. In the 4 and 6 lb. range the FC was undetectable to our camera in slightly stained water. Once you got over the 6 lb test it became visible. The larger the diameter the closer to mono it looked. Over 10 lb test I think there is no difference detectable to the human eye but I cannot speak for a fishes eye. It is hard to justify paying 9.00 bucks or even more for fifty yards when you can get close to the same performance with some of the great copolymers out there. And just to throw in a curve, I have switched to using braided line for leader material just to see what would happen and the last time I went out I caught just as many fish as the guys that I was fishing with. How this will equate to a summer run in a gin clear river I have yet to see but right now I'm tying up with powerpro leaders the fish really don't seem to mind.