I clay my windows once a year or so, and follow up with some Griot's window polish.
Z5 doesn't seem to have much of an effect on windows. Z2 makes windows shine quite nicely for a couple days, but doesn't do much in repelling water. While I like the look of Z2'ed windows, I prefer to use RainX instead.
I find Zaino works great on windows (well, really like most or all LSP's do). I frequently am hesitant to use LSP's on the windshield of other people's cars as different people like their wipers to behave differently.