Well, I got to play another game yesterday, and included some proxied Ruststalkers while I wait to buy some real ones. Let me say, I was extremely impressed. This article will do a lot of comparing and contrasting to Sicarian Infiltrators, so if you aren't at all familiar with them, check out my thoughts here.
A lot of people I have interacted with or read articles from have looked down on Sicarian Ruststalkers as being wholly inferior to their more devious brothers, the Sicarian Infiltrators. In a lot of circumstances, I could see that assessment being somewhat true. However, they really came through for me several times this weekend. The more I saw them in action and the more I think about how they did, the more convinced I am that they are just as good as Infiltrators, they just fulfill a different role.
So, the Infiltrators really shine against hordes of weaker enemies, or when they are deep in the enemy lines to mess up their shooting with their Infostatic Aura. Ruststalkers will never compete with them in these circumstances. The Infiltrators' Taser Goads will outshine the Transonic weapons of the Ruststalkers against enemies with a weak armor since they cause so many bonus hits. They will simply kill many more Imperial Guardsmen or Termagaunts (or what have you) in a short period of time. They will also probably hit first since they reduce Initiative by 1.
But Ruststalkers aren't built to kill Imperial Guardsmen. All Transonic weapons (so, all weapons Ruststalkers can take; more on that later) become Armor Piercing 2 (or AP2) when you roll a 6 to hit in the first round of combat, and become AP2 on every hit after the first round (the idea being they learn to vibrate at the perfect frequency to easily cut through even the densest armor). Pointing weapons like that against low armor hordes is a waste! The Ruststalkers are a finely tuned (no pun intended) weapon, designed to hunt and kill things like Terminators or Monstrous Creatures.
Mine made extremely short work of a squad of Assault Terminators in my last game, and I loved using them. I was concerned about whether they would get into a fight or not, since they can't infiltrate like their brothers can, but they still move plenty fast thanks to the Dunstrider rule (and they got a boost from the Terminators deep striking in midfield to try and neutralize my shooting units). It will be harder for them to get into a good fight than it is for Infiltrators, but the Infiltrators also got into a fight a little sooner than I had hoped. On a bigger board, though, this could hurt Ruststalkers.
So, if you've picked up a box of Sicarians and aren't sure how to assemble them, either option is fine. When used right, both excel. Ruststalkers are definitely intended to take on more elite opponents, whereas the Infiltrators are designed for causing mayhem amidst the enemy's line or brutally killing legions of weaker enemies. Truthfully, they are both best when used together anyway, so I'd suggest planning on getting both.
So, if you are set on Ruststalkers, read on while I discuss their gear options and further uses!
They, like Infiltrators, have two gear options that the entire unit must choose on together. The first option is their stock build; they have one Transonic Razor, with no rules besides the one mentioned earlier that gives them AP2, and a Chordclaw, which (in addition to being Transonic) has the Molecular Dissoncance rule, which gives one of their attacks every turn Fleshbane (auto-wounds on a 2+ against anything but vehicles and buildings).
As if that wasn't enough, they get Mindscrambler Grenades, which are unbelievably potent. These grenades negate the Initiative loss suffered from charging through terrain, but are also Haywire and have a rule that makes them auto-wound on a 4+. Many have called them the best grenades in the game. I don't know enough about other races' grenades to agree, but they are damned good grenades, to say the least.
Their other loadout trades all of those weapons for two Transonic Blades; bigger versions of the Transonic Razors. These lose the Fleshbane attack and the grenades in exchange for a +1 to Strength. Pretty underwhelming. These blades could be useful in some situations, but you have to lose a lot of utility for them. I would only consider using them if I had several units with the stock loadout already on the field (and even then, I just don't know if it would be worth it). But, at least the princeps can buy back a Chordclaw if you have the points.
You can also buy your Princeps a Prehensile Dataspike. This upgrade gives you one bonus attack at Initiative step 10 that is Haywire. This would be very useful for assaulting enemy walkers, or if your Princeps finds himself in a challenge with a higher Initiative enemy to try to even the odds a bit. I have yet to have it come into play, though, so I can't speak confidently as to how useful it is. If you have the points (or are fighting a highly mechanized enemy), go for it, but it's not at all crucial.
Either way you equip them, though, they get Furious Charge, making their charges even more devastating. When I counter-charged the enemy Terminators, I killed half of the unit immediately and caused enough wounds the second turn to have killed the entire unit more than once!
In using the Ruststalkers, cover is your friend! They are not a hardy bunch, with a Toughness of only 3 and a 4+ Armor Save. Their 6+ Invulnerable save is hardly going to help, since statistically if you are taking enough hits for it to be probable to save one, most (or all) of the unit will die anyway. Their Feel No Pain is more helpful against small arms fire, but it can only help them against weapons with a strength of 5 or lower since their Toughness is low.
As with Infiltrators, going for 5 man units is going to be the best idea. They aren't sturdy enough to stand up against focused enemy shooting, so having two units of five will help them avoid getting gunned down all at once. Further, few units exist that 10 of these assassins wouldn't be extreme overkill for. Many players try to leave them locked into combat after they charge so they can't be shot at in the opposing player's turn, which is much harder to do with a unit of ten!
I still have yet to use the Sicarian Killclade formation, which pairs Infiltrators with Ruststalkers to truly bring woe and lamentation to your enemies, but I eagerly wait to have enough models for it. Both Sicarian units have exceeded my expectations in game so far, so I have every intention of getting more and trying out this formation.
Anyone else with experience using these murder masters, feel free to leave your input!