There's two notable use cases for this, post-taboo.

By the Book Roland with Directive: Red Tape, or Leo with his buddy Chuck.

Fast double actions still cost one action to play (they don't cost the basic play action, but the additional cost of an action is not ignored), so it nets out to four attacks for two bucks and one action. You wouldn't really want to play it against something engaged with you, but the ability to sprint two locations away and unleash four attacks can be clutch. It's a tactic, so a single copy can sit on Stick to the Plan for emergencies.

Leo+chuck can also theoretically trigger it off-turn via Quick Thinking/Swift Reflexes/Honed Instinct, but it's somewhat unclear how that would resolve. Per the ruling for Carson Sinclair, using Rite of Seeking off-turn would eat all your actions if you haven't acted yet, but Flurry does not explicitly lose your remaining actions; it only ends your turn if it is your turn. Since it is not your turn per the same ruling (despite the confusing addition of 'as if it were your turn'), the implication is that it can be used off-turn without consuming your real turn.

This card was made for Marion.

Normal investigators are spending a card and two actions to get two actions next round, a bad exchange that's situationally useful. Marion is spending a card and two actions to get a card and three actions, two of which are deferred to next round.

Combo with The Red-Gloved Man for five, potentially six actions at base 6. Or make Keen Eye almost viable.

Just adding that this synergizes with Butterfly Swords and its upgrade, which generate two attacks per action.

Also works nicely with Breach the Door. The fighter goes first to clear out enemies, then uses their momentum to punch the shroud down to 0 to help out cluevers.

My copy of this card is marked #3 from the set (as is Fight Back!). Is this true for everyone else's copy?

200 character minimum. 200 character minimum. 200 character minimum. 200 character minimum. 20

This card, as well as its guardian high-level counterpart, is actually not that good

What is the goal of a main fighter? On the first round, prepare to fight enemies that will spawn in the upcoming Mythos phase. For that, you need to find and play a weapon. To increase the chances of having a weapon in the opening hand, fighters dedicate several weapon "slots", usually around 6. Prepared for the Worst can be used in one of the "slots", as it has a high probability of resolving into an actual weapon

This card just does not work in this setup because of that 6-resource cost. Let's consider different scenarios:

1. You drew the Thompson in the opening hand. Great, but you have to spend an entire action just taking an extra resource to play the card. You have one action left and no money. But at least you are ready to fight!
2. You drew Prepared for the Worst in the opening hand. Okay, you play and find Thompson... but you have 2 actions left and you are 2 resources short! You have no choice but to sit empty handed
3. If you use, say, Backpack to find your gun, it's even worse

So, if you want to play a gun in the first round, you'll have to find another one of your guns. At that point, it's better to ditch the Thompson altogether. If only it cost the same amount of resources as you started with... unfortunately, there's no another 0-level big gun. Took Thompson myself and regretted it, now I plan to upgrade into M1918 BAR ASAP