Warpstone Flux Rating: ⭐️⭐️⭐️ 3.5/5 stars, rounded down. The rules are quite good.
Background.
These are Veletaris who have access to unusual close combat weapons that ordinarily are not contained within the Principia Bellicosa. Perhaps they grabbed them from the elites of the rogue traders or similar.
Strengths.
The customisation here is interesting. Indeed, there is even a designers note suggestion conversions using regular Veletaris storm sections with added Necromunda weapon bits swapping.
The standard breaching shot gun is solid at S=5 with stun, but it is a short range weapon fundamentally. This can be swapped for a boarding shield and storm maul instead. This might be a good thing to help keep them alive a little bit more (even against bolt gun fire) whilst the shock maul gives a valuable breaching at S+2 (i.e., S=5). Shield wall advanced reaction might be a good thing to have in Zone Mortalis too.
The vox interlock is almost a given, and the vexilla may be wise to also take.
Weaknesses.
With T=3, one wound, distinctly average leadership, and a 4+ saving throw, the unit is not going to last long if you don't play wisely. The points cost is reasonable though, but can add up with the shields.
Despite the name, the breaching shot gun does not providing breaching!!
Builds.
10 Raiders, Vox Interlock, Vexilla (95 points).
The breaching shotgun build.
10 Raiders, Vox Interlock, Vexilla, All with power mauls and boarding shields (135 points).
Probably what most players will ultimately go for. I actually like the look and feel of this unit, even if they aren't going to last long compared to space marines.