There are three different sculpts of the basic trooper with energy rifle, sold in packs of six models.
As well as a special weapons pack with three each of two different weapons.
The backs of the models are fully detailed, which you can't see when the backpacks are glued on. With them left off they're a bit less alien looking but still pretty clearly non-human.
Personally, I think they'd also make pretty good alien combat robot types, and would probably fit in a Star Wars game comfortably as a battledroid of some kind. So, pretty versatile, maybe more so than the "naked" Crusty models are.