Funny gun and most certainly, bad.
The Colt Vest Pocket is native to a small and specific theme/archetype of who sneak assets into play quickly, it's a build based on the mechanics of cards like Joey "The Rat" Vigil, Sleight of Hand and Fence, I.E you play it quick and action free and deal the damage easily and efficiently.
A few other cards exist to support this, Fence can be used to play Pay Day, so that's a source of economy for the build. Narrow Escape can be used to play the gun when Fence or Joey "The Rat" Vigil are unavailable, certain characters might use it with either variant of "Eat lead!".
Many of the aforementioned cards, notable Joey "The Rat" Vigil, Fence, "Eat lead!" and arguably: Pay Day, are all rather shaky or outright BAD cards. Colt Vest Pocket is by no means the sort of gun that warrants doubling down on a variety of bad cards to try and make them all work properly.
If a character arises who can somehow play weapons the way Leo Anderson can play his allies, then Colt Vest Pocket will rise to recognition, otherwise it will remain on the bottom of the barrel, ready to be scraped up by folks who want to push the limits of deckbuilding.
Edit: After a little extra testing, I got to admit that a Finn Edwards deck with Sleight of Hand and Leo De Luca to get some actions stands a half-good chance to make this card shine. The free evade and extra action can give you space to safely get 3 shots from the gun, Sleight ups that to 4 shots. The card is still bad but it's passable for a 0-xp deck, they are, after all, not particularly powerful at level 0.