So far, all gangs have 1 combi weapon. It's usually something that packs a lot of punch (Eschers with a bolter pistol, Goliaths with a plasma pistol...) and another quite average (stub gun, needle gun...). In paper it's quite ok to have it like this, because if the game allowed combi weapon customization it could allow some terribly brutal combos.
My main concern about combi weapons is that they have a potential to be terribly strong because of their "dual weapon" special rule. This means that if one weapon runs out of ammo, you can still shoot with the other. It's a no brainer, but just think about the potential firepower you can unleash without reloading.