When I first saw this card, I probably had the same thought as you.
"Oh, that's cute, I guess."
This card is actually an incredible payoff for success rogue for two reasons.
Reducing difficulty is incredibly useful. Do a big skill test, this reduces the difficulty of the next one by 3, that's pretty much a guaranteed evasion or investigate on most scenarios. It means you can carry over the benefits of a big combo skill test to another one, which is real helpful if there's multiple things you need to accomplish.
Double or nothing. You use flashlight/stealth to get a free skill test, commit momentum and overachieve, then if you punch something with double and switchblade, you're attacking for 4 damage against a max difficulty of 4. (Originally 4 combat, -3 from momentum, x2 for double gets you to a difficulty of 2, overachieving requires getting at least 4) which is pretty incredibly reasonable, especially if you've drawn other stuff.
The card could be used as though it read "if you succeed by 3, your next skill test is automatically successful unless you reveal an auto fail" or "if you succeed by 3, your next skill test overachieves," so it's great as a flexible tool for setup AND payoff, which is the kind of thing rogue needed.