They are dyneema, made from saltwater fishing lines. The line on its own will float without floatant, and can be pulled subsurface if the the vertical current is strong enough to drag it down.
I suspect that it is lighter than your fluorocarbon line and probably less wind resistant. Fluoro might be hard to beat in wind, as would the titanium.
@dwalker has fished a 4.5 meter length of the 80# that he noted he could load with water to give it more weight, then false cast it out when he wanted to lighten it. The line tends to repel / shed water.
I tend to fish shorter lengths that do not touch the water. and like it mostly because of it’s visibility. I like using the end of the line as an indicator. The visibility of the end really helps when dead drifting and in subtle takes. It also has no memory so, is unspooled straight. No stretching or coiled lines.
I do fish LL but it is rare. This line is heavier than LL but most of the time I feel the minor draw that I get on the heavier line is more than a fair trade to get the other benefits. Because it is white it is visible no matter the environment, and white has been noted to be stealthy from some folk as the sky will often read as white.
this is a thread that notes it all. The only thing I do differently these days. I make a taper with a 60/40 instead of a 60/20/20.