This card starts off fine and only grows better with time. Levelled up guns can be very powerful and this card keeps them around longer, whether its a Lightning Gun or just a .45 Automatic. Dont forget that "Skids" O'Toole can use this to fuel a Lupara or .41 Derringer.
So the effect is good, worth the price even, 3 extra ammo tokens and a bit of expendable tank that you'll actually be glad to kill-off when he's empty, this means that the occupied Ally slot is less of an issue since you don't need Venturer to stick around.
To further integrate Venturer in a deck consider Inspiring Presence to speed up how quickly you reload a gun or even Calling in Favors to juggle him with Beat Cop and refund the charges. A charisma based Roland Banks deck with Beat Cop, Venturer and Dr. Milan Christopher actually plays very smoothly (And Leo Anderson similarly so with Leo De Luca).
Obviously you need targets if you pick this for your deck, firearms are the obvious target, the less obvious ones include: Strange Solution, Lockpicks, First Aid and Flashlight. There's also Painkillers, Smoking Pipe and Liquid Courage but those usually don't warrant Venturer charges.