I've heard that too. I've also heard barkeepers friend. I'm with you that I'm not totally comfortable with it. I'd imagine that it would cause tiny scratches.
I prefer to use stuff specifically for it, usually Duragloss water spot remover. It is a polishing compound that will get just about anything off, granted it takes some work and it won't take out deeper scratches.
Is a blend of cleaners and selected abrasives formulated to remove water spots from glass surfaces. Removes water spots without scratching the glass surface. Can be applied by hand or mechanical…
www.duragloss.com
I'm sure there are other people that make stuff for glass, but we used to sell this at the shop I worked at....ugh, 26 years ago......
I just never bothered to look for anything else. It does the job I need it to do. Although if you do use it, put something back on the glass afterwards, be that rain-x or a coat of your favorite car wax.
--Edit--
I guess I should say that the above is only for waterspot or heavy contaminate removal. Day-to-day cleaning I use Invisible Glass (aerosol, not spray). Probably my favorite glass cleaner for windows.
I really struggle with the Ranger. I don't know if it is the type of glass Ford uses or what, but compared to my Acura, the Ranger windshield is usually a nightmare to keep clean. And I don't mean just keeping bugs off it. Once they are on there, they're a real pain to get off. The wipers smear them, the wiper fluid doesn't do a lot of good, etc. Its almost like the glass Ford uses is more 'sticky' than others. RainX doesn't seem to last as long either. It really boggles my mind. I also have a harder time keeping the inside of the windshield streak-free, but I put that down to the types of interior plastics and the off-gassing they do over time. The Acura sits inside and is 15 years old, so most of that is gone.