Regular RainX makes the removal of ice much easier. If it was recently applied the ice kind of slides right off. YMMV.
Winner of the Deceptive Zombie OP of the Year award.
My father made an efficient de-icer. He took a metal biscuit tin, cut a hole in the side, and fitted a lamp holder. With a 40 watt bulb inside, and left in the car on frosty nights, it would stop the car from freezing up, even when it got down to -4 or 5C. I guess that in really cold places you might have to go up to a 60 watt bulb.
I typed that and then realised that those bulbs are not available here any more. Maybe a halogen?
Got that right. 
Esprix
There is nothing that I’ve ever been made aware of that people spray on their windshields to prevent freezing.
Anyway, straight antifreeze has a higher freezing temperature than a mixture of antifreeze and water. As listed in this table, a 70/30 mix of ethylene glycol and water has a lower freezing point than 100% EG. (-51C vs. -12C)
Funnily enough, there was a Frost in coastal San Diego the last couple of nights. Windshield scraping in Chula Vista and Imperial Beach.
In the UK at least there is a waxy spray that can be put on car glass that means that the Frost/ice slides off and does not stick- you just gently scrape it and it slides off.
All those cures are old school. Use Finland’s tremendous breakthrough:
Those of us who park outside (no garage) are 1) more likely to have ice/freeze problems, and 2) nowhere to plug in your dad’s invention.