I was going to post that Slugthrowers are convenient for cost and rarity, especially if your GM is putting you to the screws in terms of what you can get ahold of.
I'm having more fun playing this game in a Rarity-4 enforced part of space where I have to use a sub-par combat weapon because it's all I can get ahold of.
I'm toting around my autofire Assault Carbine with a Red Dot and it has TOTALLY made the game more challenging.
Slugthrowers are also convenient from a GM's point of view in that Minions can be given backup weapons that neither overshadow the PCs nor are desirable for looting.
When the PCs meet a Nemesis with a slugthrower of some kind, however, they worry about how tough he actually is, given that he's perfectly comfortable with a (supposedly) sub-par weapon...