The attached plastic wad on the slug might melt with the use of BP (or a BP Sub) and leave a real mess in the bores.
That's not an uncommon problem when using BP and modern plastic wads and most all plastic shotshell hulls.'
I'd use a plain round ball or a plain foster type slug roll crimped in over plain card and fiber wads. They worked fine before plastic came to be.
I've never found a plastic wad that'd stand up to the heat and not melt and deposit plastic breech to muzzle in the bore., so it's card and fiber wads only for me.
Just my 02.
