The only problem with having an SMG arm option in this pack is that your chap ends up toting an MP40 but he's still carrying rifle ammo pouches (I'm assuming that the ammo pouches are moulded on and you don't get any SMG ones).
He's got one magazine's worth, then he's going to have to hit you over the head with it. A small thing, perhaps, but some smart arse* is bound to spot that and laugh at your figures.
*That would be me.