I don,t actually have the army book but from what I have seen, getting a block of 40/50 slaves by dropping some storm vermin or clan rats could be useful to let the warp-fire thrower shoot into the melee because of the slaves special rule, could be useful before a flank charge from another source, like the attached storm vermin.
Maybe reduce one of the clan rat units and put the screaming bell in the smaller unit as a command bunker and used the dropped points for the slave block?
Maybe reduce one of the clan rat units and put the screaming bell in the smaller unit as a command bunker and used the dropped points for the slave block?