Chorus Swiss knife ( Havoc )
 Zealot Build - Warhammer 40k: Darktide 

Build Alternative:

1. If you are in need of more range ( Ether against Sniper heavy modifier, or considering a team that mostly have short to mid range weapon ) then take the Zarona Mk IIa Quickdraw Stub Revolver with mobility as a dump stat.
2. If you are the only one on your team that needs grenades ( All other teammates having ether regen or no grenades at all ) then take the Immolation Grenade. Keep in mind that doing so will stop you from having the Blades of Faith quick swap to your Artemia Mk III Purgation Flamer, if that's the case, consider using another secondary ( like the Zarona Mk IIa Quickdraw Stub Revolver or Agripinaa Mk VII Combat Shotgun )
3. If you feel like you're not using the push attack of your Catachan Mk VI Combat Blade as much, then you can swap out one stamina regeneration perk on a curio with ether revive speed, toughness or combat ability regeneration.
4. If you desire more offensive power while keeping a similar build mindset, swap Shield of Contempt with Punish Impiety.
5. If you desire more defensive support capabilities, swap Ecclesiarch's Call with Holy Cause.

Strength:

• Keeping your team alive with constant Chorus of Spiritual Fortitude use, paired with ability regeneration from curios and Invocation of Death, while staggering any enemie in the game from the same ability.
• Very good Single target damage while keeping a support mindset with the Catachan Mk VI Combat Blade, even against tougher enemies like Crushers or Bosses. Rely on push attack and Uncanny Strike for better penetration. Don't forget to alternate a few heavies to not run out of stamina completely ( A Poxburster is never too far away ). Keep in mind that No Respite will play a large part in your Stamina regeneration game.
• Will apply Bleeds easily in hordes with Blazing Piety fully stacked, which in turn will also make you crit more often with Scourge.
• Using the Artemia Mk III Purgation Flamer at maximum stacks of Blazing Piety will basically give you a better Rifthaven Mk II Inferno Force Staff until you fully run out of ammo, as Everlasting Flame will keep giving you ammo in your magazine as long as you crit ( which you do all the time in this situation ). This aspect of this build allow you to leave all the ammo to your teamates ( as long as you have a veteran, you will never need to pick up any ) and having amazing horde clear when trully needed.
• Blades of Faith will allow a very involved melee gameplay while never being pressured by Scab Trapper or Pox Hound. Even allowing you to manage Dreg Gunner and Poxburster at mid range with some accuracy. It also will keep your teams grenade economy High as you do not take any and receive one back every time you kill a specialist or Elite ( basically all the time ).
• Extremely Hard to kill between the constant Toughness regeneration of multiple perks, the mobility provided by the knife and Holy Revenant. As such, you are the best person to revive teammates or clutch a situation if needed.
•  Give constant corruption cleanse, a direct counter to any corruption modifier with Beacon of Purity.

Weakness:

• Will have a hard time managing Hordes with melee only ( mostly not an issue with a psyker on your team, but something to consider otherwise ). You do have an option with Artemia Mk III Purgation Flamer but will run out of ammo quickly if you are in need of handling it on your own all the time, which will impact your team ammo economy directly. ( be mindful of your use of Artemia Mk III Purgation Flamer no matter your team, rely on your team for most of the range fight and support them when needed, mostly by clearing hordes that the rest of your team isn't already fighting against. )
• Your only option against far away range targets are your Blades of Faith which not only require accuracy, but also will be limited ( you will also need to rely on teammates for it ). This issue stop existing the moment you swap to the Zarona Mk IIa Quickdraw Stub Revolver but in turn you completely remove your reliable way to deal with hordes on your own. If you choose an in between with the Zarona Mk IIa Quickdraw Stub Revolverand Immolation Grenade, you basically have 3 times in which you can deal with a large mass of enemies until you found new grenades ( and that's only if you do not have other classes, mostly hive scum on your team, as if you do, you are making your team lose more valuable options )
• Even so your boss damage is great ( without one shotting, you still will give very consistent high damage ), the Catachan Mk VI Combat Bladewon't make a Scab Captain shield fall quickly. ( The shield reducing damage taken from crit weapons, and taking a lot more from stagger weapons or multiple hit weapons like the Tigrus Mk III Heavy Eviscerator or the special of the Agni Mk Ia Shock Maul ).

Conclusion:

You are the best at surviving and extremely good at keeping your team alive while using minimum ressources. You have multiple options to customize this build to your liking or to your needs / team needs.
You have amazing clutching capabilities even on your own but this build is made and customized to be played around you team, if your team isn't here anymore for any reasons, you will lack at least one thing in your build.  

A great thing is, unlike a lot of builds in which you need your team to adapt around you or literally change builds / character, here you can keep the same build and adapt to your team, you're not the car, you're the engine ;) 

As it is a build made to be played around your team, if your preference is to have more autonomy, then it'll directly impact your fun, or your ability to use and master this build. 
Fun ? i would say. Again, it depends of your preference and playstyle.

Have Fun, Try it out !