Boosters are triggered after a bit time harpoon is activated. The chassis will be pushed forward. Afterwards, this gadget is discarded.
As some physics apply, the result depends on the position it is installed and the weight of chassis.
The Stronger Boosters upgrade increases the force the boosters/backpedals bring, launching you farther.
You don't have to unlock it. You only have to find them from Supply Boxes.
A boulder with two blades and a booster can be used to get over people easy. but a rocket can can also work in place of a blade.
Using a booster on a surfer/whale pushes it forward a litle, useful for melee builds.