Unlike standard monofilament line, fluorocarbon fishing line isn't derived from nylon, but from a polymer known as polyvinylidene fluoride.
One of its properties is that it has an unusually low refractive index - close to to that of water - which makes it almost invisible when it's in the water.
Wonderful news for us, not so good for the fish!
And there's more ...
Clearly then, it's good stuff - but its greatest attraction to us anglers is its near invisibility in water.
But it's expensive, so if you regularly fish in murky water like the Thames Estuary - or at night - then don't bother with it. Stick with the less expensive monofilament fishing lines, or braid fishing lines as for you, fluoro lines won't represent good value for money.
But for those of us who fish in clear waters, my view is that the major benefits offered by fluorocarbon line justifies its high initial price. After all, anything that helps us catch fish ...
Use it for hook snoods, the line in terminal rigs, and as leaders for plugs and crankbaits - but not with topwater lures, as fluorocarbon line sinks and will spoil the action of the lure.
I now rig all my lures with fluorocarbon fishing line when trolling in the clear water of the Caribbean, and while I can't be certain that it's improved my catch rate - maybe I've just got luckier - it seems that way to me.
So, to summarise ...
Not so good
Just one more thing ...
I've heard some anglers say that they've had problems getting knots to hold in fluorocarbon fishing line.
I use the Uni-Knot, or crimped connections in heavy line, and have had no such problems.