Window Deflectors

do not know about the prius c specifically, but on other vehicles they just aid ventilation, keeping the rain out when widows are down about an inch either while driving or parked. They have increased wind noise a bit in my experience.

 

In my case I felt the weathertech ones I have made the wind noise a bit louder, but I don't have anything to compare them to. I feel they do a decent job keeping the rain out while driving though.

 

I recently bought and installed the Weathertech visors, front and back, and I was disappointed at increase of road noise. I also didnt like the fact that the window motors had to struggle to fully close the window since the weathertech versions are in channel.

 

I had issues with closing the windows at first, but they settled into the channels after 5 or so open and close tries. It did take some wiggling to get them in the "perfect" spot though.

 

But they change the look of the car too, they make it look pretty cool....

 

My WeatherTechs didn't increase noise that I could notice, but they always seemed to move when the window was up or down.

They came off two months after I had them. One cracked taking it out. Keeping the rain out was nice though.

 

The Prius C is a loud vehicle. The wind noise is pretty bad at highway speeds, and the Weather Techs I installed don't seem to make much difference with noise. The benefit is rain staying outside when the window is not fully closed.