Most cars have wipers on the front and back windscreens, and some even on the the headlights. But you'll be hard pressed to find a vehicle with wiper blades on the side mirrors, which get just as wet and obscured when it's raining.
They're flexible enough to conform to the shape and contours of most mirrors, and they attach with a simple strip of 3M adhesive so you can easily apply them in a parking lot, even from the inside of your vehicle. There are no tools or custom installation required, just a basic level of hand-eye coordination. [Fancy]