The new Hymnal Types in this set are useful, and I love some of the Organization Rolls, but I think my favorite part of this is the Arcanist Upgrades.
That said, not all upgrades are created equal. The Hellfire Driver is quite useful, but the one I'm likely going to use the most, both as a Choir Master (GM) and as a Player, is likely Megiddo Mode. That mode also seems the closest to my favorite upgrade from Symphogear, the Ignite Module.
If and when I run a campaign as Choir Master, I will probably have a veteran Hymnal Pilot as a GMPC with a few basic upgrades plus Megiddo Mode, if only to give the players a goal to surpass and maybe some assistance on deadlier fights. :)