Whichever product you choose practice on a few windows. I know for myself I thought the thinner the better but that didn't prove to be true. It was much more dished/ concave when I tried for real thin and worst case it developed a hole as it dried. Not enough material to take up the shrinkage, I guess. Somewhere between too globbed and too thin is a sweet spot that lays pretty flat and the extra thickness doesn't seem to hurt the clarity. Also, get it where it looks decent and then leave it alone. It tends to smooth itself as it dries.
When doing an auto finish where shine was desirable I also clear gloss coated the whole thing, windows and all, as an experiment. That was probably the best, clearest windows I've ever gotten. I will do that again.
