Been using it for 20+ years, maybe into my third bottle. It doesn't go bad with age. The trick is to get your windshield good and clean to start. apply per instructions, buff it in well and do a second coat the same way. Yes, it does take a bit of elbow grease. Spritzing with a little watter before you buff helps. I seem to do it 2-3X/year on the windshield, ix/yr on the sides & rear glass. Ice, frost, snow just pops off in winter with rubber squeegee, next to no scraping req'd.
I've also used it on the clear plastic headlight covers, works OK but Meguirar's plastic cleaner & polish does a better job, as does Klasse All-in-one.