Bill, Z2/Z3/Z5 are all prolymer protectants. None of them are polishes. They are sealants. Z5 just has some minor swirl filling capabilities.
I choose Zaino for ease of use and durability. No Zaino is not compatable with GEPC (in terms of putting Zaino on top of it), some people use Klasse AIO with Zaino, I do by using Klasse AIO on my rotary with a foam polishing pad to remove swirls and light oxidation and put the finishing touches on a car that doesn't deserve a PC follow up, a dawn wash, then Zaino away with Z1 or ZFX with Z2/Z3/Z5.
The paint has to be as close to perfect as possible before starting the Zaino process. It can take a good protion of you're day getting a car Zaino'd but after that its just easy and simple upkeep/more Zaino layers.