** If you're planning on a minimum unit of Vulkites, take the shields to have a better chance at surviving combat. Also, don't forget that they have a suicide ability but it is only once per game. So you better be sure you use it wisely and not to waste it on combats you know you'll win.
**Other philosophy is Shields for 20+ man units to tank objectives while 10 man units have dual axes for better damage output.
**Overall, the Vulkite Berzerkers fulfill the role that they have to: even though they are a little bit expensive at 160 points (as they have a watered down version of the No Respite ability of the Khornate Blood Warriors, and there is no point discount for having a lot of them), their superior damage output (rending attacks and mortal wounds on the charge) and overall army synergies (several ways of improving both their damage and survivability) put them exactly where they should be.
*'''[https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/AoS_Fyreslayers_WSCards_Auric_Hearthguard_EN.pdf Auric Hearthguard]:''' These are probably the best unit in the Fyreslayer list. The normal Dorfs have Irondrakes, who are almost universally acknowledged as one of the most powerful ranged units in the game. Auric Hearthguard are about as killy with their great big Magmapikes, which make them halfway decent in melee and utter murder at range, with 2 shots each at 4+/3+/-1/1, Keep in mind now that most ranged units lose efficacy if they move or enemies are too close. Auric Hearthguard doesn't. They can charge right in and finish the job if their shots only almost killed something. And in addition, they can use their shots to trap enemy monsters in magma, halving their movement and lowering their Hit rolls.
*'''[https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/AoS_Fyreslayers_WSCards_Hearthguard_Berzerkers_EN.pdf Hearthguard Berzerkers]:''' (120 pts, min 5, 400 pts, max 20) Per the new Battletome, Hearthguard Berzerkers may have arguably seen the biggest improvement out of the whole book. Hearthguard have a nifty ability to ignore wounds and mortals wounds on 6's, and this is increased to 4's when they are within 10" of another Fyreslayer hero. In addition, Hearthguard come with two wounds and two attacks base on all their weapons along with 2" reach. Their Berzerker Broadaxe has better Rend and damage than the Flamestrike Poleaxe, but the Poleaxe has the potential to deal 2 Mortal Wounds on top of normal damage on 6's to hit. Poleaxes are better against 2+/3+ saves and marginally worse against 4+, where Broadaxes start overtaking them. Overall, a very powerfull unit that surpasses Vulktite Berzerkers, while maybe lacking some of the reliability of Vulkites thanks to their better armour save in combat and ability to attack after perishing. The Hearthguard Berzerkers are there to smash through any enemy lines and tank enemy attacks with their extra save after the save. Always remember to keep a hero nearby at all times as they lose a lot of their surviability without it.
** Don't forget we have easy way to give 3+ save (Battlemith + prayer), and even 2+ with the Runesmiter. Now take a unit of 20 (they have the horde reduction cost, unlike Vulkites...); with a 3+ (or 2+ for 1 turn) save and a 4+ FnP, they will not die easily, and they will hit like a truck in return: 2 attacks each 3+/3+/-1 2d, with a range of 2", they can fight on 2 ranks... this is borderline nasty (without even including our runes, you know like rerolls hit roles of 1 or add -1 to Rend...). And you can even give them rerolls all failed wounds rolls, and making them attack twice in the combat phase with a Battalion (if anything survives the first wave to begin with).Vulkite and Auric are good, but Hearthguard Berzerkers are really, really, good. And oh, we can make them battlelines with a Runefather as general.
*'''[https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/AoS_Fyreslayers_WSCards_The_Chosen_Axes_EN.pdf Chosen Axes]:''' The Fyreslayer Shadespire Warband. Required to be taken with Fjul-Grimnir. For 40 points you get 3 Duardin, 1 with 2 4+, 3+ Rend-, 2 Damage Attack (rerolling to hits), 1 with 2 4+, 3+, Rend - 1 damage attack (also rerolling to hits) and 1 with 2, 4+, 3+, Rend -1, 1 Damage attacks. They also never take battleshock and get +1 to wound when within 3 of Fjul-Grimnir. Unfortunately, they only have a 5+ save and a 6+ FNP, and for only 3 wounds, that's not a lot. Given that they cost the same as 1/3rd of a unit of Vulkite Berzerkers, it's hard to justify taking them, and thus hard to justify Fjul-Grimnir.