Focused Firing is the first upgrade for Path 1 for the Dartling Gunner in BTD6. This upgrade increases the accuracy of the Dartling Gunner by decreasing the random projectile deviation from ~8° (?) each side to ~6° (?).
It costs $255 on Easy, $300 on Medium, $325 on Hard and $360 on Impoppable.
Purely for providing extra accuracy, it is helpful for the Dartling Gun to specifically be more accurate against longer distances. When paired with Faster Swivel, the Dartling Gun becomes optimized for both micromanagement and reduced randomness, but it sacrifices potential for camo detection or internal extra attack speed.
Purchase Focused Firing if shooting at longer distances is a priority, as it helps with making shots more accurate across long distances.
Focused Firing is less effective for Buckshot and its upgrades. While it theoretically helps to improve upon the potential for multiple projectiles to hit a single target, important targets such as grouped bloons or MOAB-class have large hitboxes where they can be damaged. Faster Barrel Spin provides both consistency in shots and more firepower overall, and also comes with the benefit of having camo detection.
Focused Firing with Hydra Rocket Pods is useful for allowing the Hydra Rocket Pods to shoot along straightaway lanes more reliably, but it takes away the potential to add extra explosions.