I have some old Orvis braided butt leaders that I never used until last season.
They work kinda like a furled leader in that they are very supple (and spray water
You add a tippet to the short mid mono section. The braided butt itself is only the butt section, probably only 1/2 -2/3 of the whole leader
The lead core ones are for adding a 'sink tip' to a floating line. Very handy