I hit some very serious rain in Iowa in early Sept (after Wing Ding), for HOURS. I had sprayed my (Neotec II) shield with Spray Away early that morning to clean off the day before bugs. Seemed to help a lot with the rain running off, something I was not expecting. I look over my windshield by a few inches, so I guess the air flow helps.
Don’t know about the above mentioned recommendations but will add that I’ve used Mequiars “PlastX” a cleaner and polish. Going on 20 years and do notice that rain will bead up and run off with wind assistance. Also noticed that it extends the service life of my visors and shields. This rides in a side pocket of my tankbag along with a microshield cloth.
I've had good results with Cee Bailey's Rain Repellent Max for years, it's just like Rain x .. but formulated for plastic... just spray on, let it haze and buff out. The only downside is that for a long distance ride in the rain you will need multiple applications.
Most of the products I have seen appear to be some form of silicon and/or a soft liquid wax, some may have a solvent that is not good for plastic. I prefer a wax product that glazes over and has to be buffed. It seems make bug removal easier and beads rain water.
I typically use Lemon Pledge furniture polish on my windshield. Does a good job cleaning and getting the bugs off plus the water beads. I'll cleam my windshield with it every few months whether it needs it or not
There always exceptions, I got caught in Trop Storm Imelda. I seen it rain like 6 inches in 30 minutes...lol. Ive used plexus, furniture polish, rain x they all require a wipe from the left thumb of my aerostich rain glove.