I've been playing with Co-Focus off and on since last summer, and yeah it's hard to beat. I've recently found something that fits my specific needs a little better. I'm absolutely sure Polyfiber HiTec 18 is more comfortable than Co-Focus 1.18. I'm saying this with certainty because I have been trading off with both set ups, at identical initial tensions (58/53) in identical frames, from the same package of gut mains. A bit more tension loss, but is still right in line with your average poly. That's a good trade off for me. I've got more to try, but it's the one to beat so far.