I've found 845 to be good for 3-4 months on a garaged car. It may last longer, but I wax every season regardless.
It hasn't fared as well on my outdoor beater, but it's still better than a typical wax.
The only thing about working with 845 is the need to treat it like a baby's bottle, either by warming it up in the sun, or a water bath, so that it liquefies. Otherwise, it's a soft goop.
I'm curious about Fast Finish. If it lasts even half as long as they claim, and is so easy to apply, it sounds perfect for the beater.