As far as I know there is a difference between FC leader and FC line
The FC leader has a harder outside shell for abrasion resistance and the FC line has a softer outside shell for casting ability Some of the cheaper FCs are somewhere inbetween
I use sunline FC Rock for leader and sunline FC sniper for some spinning with HBs
For flatties when you used to use 20lb mono for trace to stop bite throughs you can now drop down to a 12lb FC leader because of the increased abrasion resistance