I've got pretty much every gun I need, my 5*s are:
Polaris
Blitz Needle
Storm Driver
AP
Sentenza
So I'm wondering if I should even bother getting a Callahan. I'd much rather demolish a group of devilites or wolvers with my Final Flourish. If someone can convince me why a Callahan is worthwhile then I'll definitely get one.
I'm mainly gun just for PvP with this set up:
Nameless Hat
Justifier Jacket
2x Pentax Heart
Storm Driver
Sentenza
Polaris
Yes...
You can deal with devilites with an FF, and most likely experience pain while doing so... or you can easily take care of them with a callahan. Once you get a rhythm of move-shoot-move, the Callahan is probably the safest way of dealing with devilites.