... to the party, Jim, but thought I would chime in.

I haven't used fluoro leaders or tippet much since virtually all of my fly fishing is with dry flies, with an occasional outing with streamers, and a rare exception fishing nymphs. I don't use fluoro with dries, because they tend to sink the fly, especially the smaller ones. I fish streamers with a Type II full sinking line so there is no reason to waste money using fluoro.

When I have used fluoro, the simple ( not improved ) clinch knot has worked just fine. I typically use a four turn clinch knot.

One anecdote about fluoro and clinch knots. Back in April 2016 I was fishing a northern Idaho freestone river using some Orvis 0X fluoro tippet tied to the tip ring of a homebrew furled fluoro leader with a four turn clinch knot and a J.A.R.S. nymph with the same knot. In a little under half an hour, I hooked up two B run Clearwater River steelhead trout and landed both. Both of these fishies were in excess of 30" and it took about eight minutes to land each of them. The four turn clinch knot held up just fine.

John