Take it when you want the fear game with jump packs attached. This is the important distinction in the Chaos lineup: Nightmare Hunt is a bigger detachment rule, but it carries the NIGHTMARE tag and so cannot be combined with Murdertalon Raiders. Dread Talons carries no tag, costs the same 2 DP, and pairs with Murdertalon Raiders for exactly 3 DP.
Be clear-eyed about the limits. A -1 to Battle-shock tests is a real but indirect effect: it does nothing against an opponent whose units are at full strength, and some armies barely take Battle-shock tests at all. Three of the six stratagems only pay off once something is already broken, so a slow start compounds.
Sample gameplan: spread Heretic Astartes units so the 12-inch aura covers the centre of the board. Shoot to push units below Starting Strength, and let the Command-phase clause do the rest. Put Eater of Dread on a rear character to bank command points, Night's Shroud on the Chaos Lord holding your objective, and Warp-fuelled Thrusters on the jump Lord leading Raptors. Spend Pitiless Hunters on the broken unit, Bloody Example the moment you kill a Character, and hold Merciless Pursuit for anyone who tries to disengage.