Let's see.
- Keeper USB: It's a great buff, but I'd still use him, if at all, for wall. On the other hand, I could use him for this and Y'shtola for wall, so... Maybe.
- Ashe BSB: The queen of Lightning meta. Admittedly tempting, although now that I have her OSB, it's a bit of a toss-up. That said, her BSB is more functional than her OSB, so... Maybe.
- Rosa BSB: Have it. It's nice. So, nah.
- Edea BSB: It's pretty nice, true, although I have Serah's BSB for my Ice BSB needs. So... Maybe.
- Sabin SSB: Meh.
- Palom SSB: Very nice. However, I already have BSBs for two mages in IV (Rydia, Golbez) so I'm not sure this would tempt me to put him in my IV caster slot. Versatile for a one-shot, and powerful, but... Just maybe.
- Fran SSB: It's just weird, you know? It's like... Why is this even a thing? She can't exactly take advantage of it. Anyway, I have her reverse wallbreak SB, which is actually really useful and fits her, so... nah.
- Laguna SSB: Nah.
- Edge SB: I have his instant pBlink/Hastega/Last Stand SSB, so why do I need this? Nah.
To me, it depends on whether it's an LD. If it is, absolute yes. If it isn't, there are some solid maybes there, but also some nahs. I'd probably skip, frankly.
Yeah, skipping the fool out of that.
Side note, if you haven't gotten your raid campaign mythril already, do it. It's super easy. Just start an easy-level Leviathan campaign with your two best Lightning casters and run it as soon as someone joins. You don't need a full party, you don't need the highest difficulty, you just need to clear it three times. It's basically free mythril.
And a stamp.