I cannot recommend Rainex highly enough. Never occured to me to put it on a visor, but that makes perfect sense.
I love the stuff, couldn't function without it.
I used to run a taxi business in the blue mountains and had a set of wipers on one of my cars fail on a friday night, with rain falling and forecast for the weekend. None of my drivers would drive the car without wipers, so I did some swapping and ended up driving the car all weekend myself, just using rainex.
Got a few queries from passengers, but told them I was a test vehicle for a new windscreen product. They all thought it was a great product.
Had no visibility problems.
Wouldn't recomend removing wipers from cars, but it got me out of a spot.