Way back when Fluoro first became available I gave it a try, decided I didn't like it and went back to the Hardy Copolymer material I'd used for years for leaders.
More recently Hardy seemed to mess about with the Copolymer material they made and it seemed to vanish, then reappear, then get rebranded and so on. I thought this provided another chance to give the fluoro a try and I've been doing some testing for about 3 seasons now.
I normally fish 2 flies on a cast in, basically, the traditional wet fly style and because of wind (and let's be honest I'm a bad caster) I often fish quite heavy leaders. Some years back I took a visitor out for some Lewis moorland trout and she wanted to know if she should use 3lb or 5lb leader material and was totally stunned when I announced that I was going to use the same 15lb leader I'd tied on for salmon the previous day. Now she didn't have local knowledge etc. so it would be expected she might not do as well as me but the fact that I had a lot more fish than her for the day certainly gave a clear indication that the 15lb material wasn't a major problem.
The more I fish with the fluoro, and the more people I talk to on the subject, the more convinced I become that it has some serious problems and that its performance may not be completely understood. This last season I lost a Lewis spring salmon in a mystery break plus I lost a sea trout where the leader (15lb BS, probably 2lb sea trout) broke with almost no pressure in the middle of a flat bit of fluoro well away from knots etc. I've also talked to a number of people, some who fish a lot more than I do, who are also moving away from fluoro because of unexplained events such as those I mention.
Recently, after some discussion with a Lewis angler, I've decided to give the yo-zuri material a try. It claims to be a copolymer of fluoro and nylon and, even better, it costs about £7 for a 275 yard spool. I haven't fished with it yet but it seems like nice material to handle and it is relatively stiff, which is what I want.
For a bit of fun I did some testing - I took some 7lb BS fluoro (Riverge) and put a simple overhand knot in the middle of it and pulled it apart. It came apart quite easily and with a pull rather than a good tug. I then did the same with some 6lb yo-zuri and even with a good tug couldn't break it as it was cutting into my fingers and was becoming quite painful. I then did the same with 12lb fluoro and found that it broke with a sharp tug. Not science, I know, but interesting.
So far I've been impressed with the yo-zuri in terms of my simple tests so it will be interesting to see how it fishes as the season goes on. I'm pretty relaxed about my fishing as I've caught about as many fish as I need for a lifetime but it must be said that I would be reluctant to go back to the fluoro at this stage and it seems to me that it might not be the material to use for the fish of a lifetime, yes it works well a lot of the time but everyone I talk to has had "unexplained failures" of some sort. Of course I'd had breaks before going to fluoro but I could always offer some reason, usually I'd done something stupid, and this has not been the case during my testing with the fluoro.