In theory the advantage of the improvised cards is twofold: one they provide a "skill-bonus" in the form of a test difficulty reduction, and secondly they provide action compression when played from the discard by allowing you to double the action (gathering two clues for Winging It and dealing two damage for Improvised Weapon).
Impromptu Barrier does fine at providing a skill bonus, though there are very few evade 1 enemies and so you are pretty unlikely to get the "guaranteed success" that difficulty reduction can sometimes provide. A resource and a card to get effectively a +1 to two evade tests is probably a bit worse than the same rate on investigating and roughly the same as that rate on combat, purely based on how frequently tests come up. So on that front barrier isn't too much worse than the other improvised cards.
Where the card really falters for me is in the second effect. Doubling up on a combat test is frequently valuable, Improvised Weapon allows you to deal with a three health enemy in two actions, or split its effects and deal with a 1 health enemy and a two health enemy at one action each. Winging It lets you double the most important action in the game, working like a survivor version of Deduction. Doubling up on a successful evade action is simply less valuable than either damage or investigation as rather than requiring a two clue location or two health enemy (both very common even in solo) it requires you to have two enemies at your location, and for you to want to evade both of them.
If this card simply let you evade a second enemy at your location without the X or lower requirement, I think it would be niche but playable in investigators who like to evade a lot and can struggle to deal with multiple hunters. As is, not only do you have to want to evade two enemies at the same location but you also have to over-succeed by enough to evade both of them, otherwise the card essentially does nothing and you wasted your resource.
It's a real shame since I feel the other two are really home run designs and it would be nice to have a solid third to round out the set but, but I feel this falls more than a little flat.