I tried Expel on a whim a couple times. It's fairly expensive IMO per application, and one applicator does not go far. On my little beater 2001 Kia Spectra that I once owned, I was lucky to get just the windshield coated and the front side windows partially coated with what little "vapors" there was left.
You have to work at breakneck speed to apply Expel, and since is seems sort of "thick", one has to again work quickly to smooth level and eliminate streaks.
As far as longevity, I noted no greater longevity than Rain-X, and no matter what I did as prior prep, I won't be ever purchasing it again.
Rain-X, inexpensive per application, no crazy prep prior to use, just clean windows first, apply either directly to glass and spread and massage in like a wax, or spray upon a folded piece of paper towel to apply. The latter method will insure you don't get overspray spatter onto the paint, or other areas of the car.
Plenty of time to work with Rain-X. After application, let sit to dry about 10 minutes, first use a water dampened clean towel to buff and remove the majority of hazing, the take a clean dry MF Towel to finish polish all outer glass.