From my understanding, it basically creates a "vortex" (hints the name!) of air making a spiral type effect, which in turn creates better/more effiecent air flow to the spoiler, which will help create better downforce at higher speeds...which ultimately will help make the car more stable, and the rear-end more staionary. It goes along with the theory of spiraling airflow is more effiecent than non-spiraling.

Like everyone else already mentioned, on a base Lancer, the only benefit you will see is aesthetic. And yes, they are fairly difficult to install/remove. I would just leave it be if it was me.

Hope this helps, or made sense...I didnt feel proofread lol.