the gun halberds make complete sense to me.
Who else uses them? Custodes! who are they? Why, the holy angelic guardians of the emperor, Legends in themselves, beings of such heroism and might that they are seen as near angels to those that hear of them from the priests of the imperium.
It makes complete sense to me that a band of religiously driven nuts would try to emulate the custodes , modelling themselves as bodyguards to the faith and the emperor by proxy.
but they have to do it in their own ramshackle way.
I really like the kit. Even the really odd stuff like the crossbow grenade launcher makes sense to me. Poor extremists cobbling together what they can from stolen scraps. you don't need to look too far today to find examples of protesters and extremists alike cobbling together catapults to take on riot police, or using fireworks as improvised grenades.
BUT since I don't play necromunda, these guys are going to be made into a grimdark brettonian men at arms unit who follow around my stormcast hero.