Have been using this product for years.  It turns the raindrops to small beads that floats upward on your windshield, not downward as the raindrops would.  Entertaining to watch, as well as very effective.  When the raindrops stop beading, it's time to reapply. Very easy and quick to reapply.  In an emergency (wiper failure), you can actually  see well enough to drive safely, as long the rain is light to light moderate.