Inspired by the entire "everyone runs Feirros+Leviathan" discussions - what might be hidden gems that may not be that famous, but still more than usable with our supplement?
With the models around anyway, I intend to try Tarantula sentry guns. They are a staple for my Raptors lists, denying large areas for deep strike while thinning chaff ranks, and a nice speedbump for the more aggressive armies. In our case, they make better use of Feirros' targeting array (at usually BS4+), resulting in that nice rerollable 2+ to hit. Automated Targeting might still make them a bit unwieldy, but it's a cheap way of spamming more heavy weapons.
Twin assault cannons, on a unit of 3, racks up 192p for 12W T5 - which might not be the most resilient choice we have, but averages 35 hits S6 AP-2 per round, or 14 hits in overwatch (without CM around), making it near suicidal to charge with the usual 10 GEQ squads or 5 MEQ squads. The cheaper heavy bolter variants combined with a single twin lascannon works too, being considerably cheaper and packing AT as well as anti chaff.
Bonus points for their ability to entirely ignore the fact that someone is within 1" of them. Not only can they still fire unimpeded (yes, at the very unit currently hitting them), but also your remaining army can shoot that target too. I've had more than one opponent run their units into CC with a tarantula to save them from getting shot, only to get shot by both the tarantula and everyone around. With their base size, that's also a nice wall to block movement/CC.