Saesborne's Non-Conventional Auric Maelstrom Stealth Zealot (AKA London Homeless Build)
 Zealot Build - Warhammer 40k: Darktide 

TL;DR: Stalwart offers a ton of survivability, Invocation of Death makes you able to spam Shroudfield extremely frequently, while Blazing Piety itself offers even more consistent critical hits. Then, you just use the knife the way you would normally. 

This is the most comfortable auric maelstrom knife build I've made based on my personal experience in my 600+ hours of Darktide gameplay, which I'm having even more success with than the warp-cursed dueling sword. 

Despite how this build isn't all that difficult to master when compared to the conventional Inexorable Judgement knife build, you'll still need a very solid understanding in melee & maneuvers for this build to work. 

I'm personally not a big fan of MLA formatted essays and all that Administratum-approved stuff, so I'll try to explain things as plainly as possible. 

First of all, let me each explain the reasoning behind the seemingly controversial takes in talents:

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         1. Why Blazing Piety instead of Inexorable Judgement? 

This is arguably the first thing you'd notice when looking at the talent tree for this build. 

Yeah, why ditch the conventional mobility-focused Inexorable Judgement, and pick crit-focused Blazing Piety instead when playing with Shroudfield? 

There are several reasons: For one, to make full use of Inexorable Judgement, you'll first have to be extremely good at timing your dodges and movement to stack it, which isn't exactly easy to do when auric maelstrom throws one clown car after another at you (with waves of specials seeking to lay a Mini-Exterminatus on your team as an Isstvan-III type awesome cherry topping), on top of how inconsistent Inebriate's Poise proc sometimes. Thus, reaching stack 15 is only easy on paper, not something you'd be looking forward to when it really comes to maelstrom level skirmishes. 

Now, for the pros of Blazing Piety: 

By picking Blazing Piety, you'll first gain access to Invocation of Death, zealot's most reliable cooldown reduction talent that pairs extremely well with knife's high crit chance. Then, combined with the +15% Critcal Hit Chance from Blazing Piety itself alongside Scourge, you'll be proccing crit nonstop. Meaning that you can activate Shroudfield practically EVERY 10 SECONDS. Way more efficient and accessible than whatever that grox-turd of a skill Pious Cut-Throat is. Thus giving you the ability to literally turn the battlefield into your playground Night-Lords style (or Raven Guard), either escaping the most devastating siege of melee elites or slit the throat of every gun-wielding treacherous veteran you see in the most horrifying way possible. The heretical ones, of course. (Don't actually kill the vet in your team)

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         2. You don't have the classic Dance of Death/Thy Wrath Be Swift/Good Balance combo, will that be an issue?

Short answer: No. 

Long answer: For the survivability these 3 talents offer, we already have Stalwart and Enduring Faith, which are already more than enough. Especially if you think about how often you'll be proccing the latter with the crit chance you'll get. (Also the reason why I'm running only one toughness curio) 

Then, Dance of Death just don't work as we're running Artemia Mk III Purgation Flamer with Everlasting Flame as a compensation towards knife's inferior dense-horde clear. (Also very useful to just stragiht up cook everything non-Crusher in a mixed horde within a few seconds, reloading is an non-issue because EF just works) 

You can't expect recoil and spread reduction to work on a flammenwerfer. Amirite Hanz?

Also pro tip: Using your throwing knife while you're taking out the flamer will instantly remove the draw animation, thus allowing you to start cooking things way faster than normal. (Also works on bolters. Especially on bolters.)

Thy Wrath Be Swift isn't all that necessary as well. Neat? Yes. Necessary? No. Because you're using a knife. You're not gonna worry about having your attacks interrupted because you have unparalleled mobility, unlike one of these Space Guts with a Relic Sword busy tearing an entire mixed horde to pieces face-on Tyberos style. 

As for Good Balance...sire, you already have Stalwart and Enduring Faith, we just talked about this. 

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         3. I need my IJ attack speed boost! 

Fanatic, you already have Faithful Frenzy. 

In summary: Quick wits, fast hands. Got a problem? Knife it out. Or tank it as long as its not a crusher overhead.