Faster Swivel is the first upgrade of Path 3 for the Dartling Gunner in BTD6. It allows the Dartling Gunner to rotate at twice the speed. For comparison, a Dartling Gunner without Faster Swivel takes up to 2.0s to rotate towards the direct opposite side, but with Faster Swivel it now only takes 1.0s to rotate at the same angle.
It costs $130 on Easy, $150 on Medium, $160 on Hard, and $180 on Impoppable.
While a cheap upgrade, Faster Swivel can be useful in situations where there are multiple sides for the Dartling Gunner to target at, making it useful on simultaneous split-lane maps such as Spring Spring, Pat's Pond, or even Bloody Puddles. In this way, the quicker turning speed allows the Dartling Gunner to quickly target new locations much sooner.
Alone, this upgrade isn't very useful in most situations, but it can be helpful for specific situations where micromanagement around corners is needed.