We use the orange -25F RainX stuff year-round. Seems to work a little better than average, doesn't freeze. It has a very, very mild "coating" effect that sorta kinda keeps the windshield beading water, so you do end up using the wipers less at speed. It's much cheaper at Costco.
Life is waaaaaaay too short to fart around with mixing up your own juice or changing it for the seasons.
That said, there are places where the formulas are restricted, and so you have to mix up your own. Or you might live in an area that doesn't get cold, but you have to boost or change it if you go somewhere cold. Bit of a pain.
Even in Indiana, you do occasionally see cheap "summer" juice for sale, which freezes in the winter and causes havoc for cheapos who aren't paying attention to what they're buying. Most of it around here is the -20F stuff.
I really do get why you don't want to just go spritzing toxic methanol and such into the environment, but then again crashed cars can do a lot of environmental damage.
One thing that really frosts my Cheerios is that on the rare occasion I've paid someone for an oil change, they sometimes top up my nice clean expensive orange washer fluid with their crappy blue cheap generic stuff. Bleah. If I think of it, I try to top it up beforehand to keep them out.
