- "As If": This was added to the FAQ (v.1.7, March 2020) and then amended (v.1.8, October 2020). You can read the October ruling on the ArkhamDB rules page here. (I'm adding a hyperlink rather than retyping the rules in case in future the ruling is changed or amended - at that point, the rules page will be updated and all ArkhamDB FAQ entries will link to the correct ruling.)
Fast. Play during any investigator's turn, except during an action.
Immediately take an action as if it were your turn. This action does not count toward the number of actions you can take each turn.
TL:DR, nice effect, there is not a character around that doesn't want this in their deck. Problem is that a free action, at that cost and a cardslot, probably not be what the doctor ordered, therefore it'll rarely see play.
Swift Reflexes is a free action, it even gives you some leeway in when it happens, sneaking actions into someone else's round, useful for example to grab an enemy or snipe a persistent encounter card so that another character might do their thing better. An extra attack, a move, actions are good.
But the problem is the economy, you get 3 actions per turn for a dozen+ turns every game "for free", paying 2 resources and a card is steep but fair, but can you spare the card slot?? You need those slots to build that carefully orchestrated deck, how valuable is that lone bonus action over, say, an extra card draw from a boosted action with one of the neutral skills on it? Do you have enough weapons? Most cards are about generating extra success value from every action, "More success in less actions", a flat +1 action is therefore weirdly often unhelpful, at such a steep cost that is.
It's not a bad card, it's mostly a case of an effect that in of itself is so small that I wonder if it'll be worth it's slot, at that price too. I would be glad to see an XP version that grants some bonuses during that extra action.
Edit: Some more experience.
I started finding more use for this card, mostly outside the faction. folks tend to pay through the nose for stuff, especially , which is where non-repeating extra actions really shine. Characters with large bonuses already will find Swift Reflexes much more routinely useful then those with 3 or less. Tony Morgan and Leo Anderson for example.
2 resources and 1 card for 1 action, but 2 cards and 1 card worth 3 actions, so 3 actions for 1 action? Not an impressive card among all those rogue cards providing action. But when export to other factions with Versatile, this ability become priceless. Seekers draw cards so easily, that you can almost consider cards as free. So 2 resources for 1 actions now? If there is any card can get resources as efficient as 1 action (you don't have to count in any cards spent!) for 3 resources, then the combination will become 1 free resource! And then you just use the free resource for more actions! Here is a deck for example.