Since I've had my Givi I've tried a couple things. Plexis for one. It gives a nice shine and easy as pie to use but doesn't shed the water off the windshield nicely. I do like it for a quick shine on the plastics though. Also tried a liquid wax -- forget the brand -- it's also very easy and beads water like other waxes. Trying to stay away from anything that brands itself as a "cleaner" wax or polish.
I'm in the process of searching for waxes/polishes that "sheet" the water off. I remember a product advertised heavily on TV ten years ago that advertised just that. I got some at the time and sure enough that is what the water does -- sheets off leaving no beads or anything at all. Of course I can't remember what it was! Never tried it on the windshield at the time -- only the car's paint. Didn't give too good of a shine so I didn't buy more.
Anyway, I've found a few by searching "polish, water, sheeting" just today and going to search some more. Maybe it's what we need for our Givis. I guess somebody will have to experiment.