No armour bane just Str10
No assassins are not unique....provided you're allowed to take multiple detachments (i.e. Standard rules) you could take 3 vindicares and a couple of Culexus though be around 700 points for 5 models with 4+ saves
Been rereading the Callidas rules, basically she has precision strikes on a 6 to hit, 6's to wound are "phasing wounds" which ignore invulnerable saves.
The template pistol no longer tests vs. Ld just a straight up AP2 template that causes wounds on a 4+
Callidus also can choose to attack with poison blades instead of the phase sword, they're poisoned 3+ with rending