Edwin-it really isn't the time factor, it isn't that much. I just prefer ready to use products and I hate wasting product. I don't really desire to put more than 1 coat of any LSP on a car in one session unless specifically requested by the customer but it is my understanding you need to use ZFX with the first coat and if I am only applying a single layer, I need to be very precise when mixing to make sure I don't waste anything. I just wish Z2 Pro was ready to use (and layer if desired) right out of the bottle, without having to buy another product and mix it in.
Like I said, I really like the appearance of Z2 Pro, but I also like how other products look too and for me, the one that is the easiest to use and gives me the results I want is the one I use.
If it was my own car and I didn't have black, I'd be more inclined to use Zaino and layer it since I'm not as concerned about time and don't need to charge myself for the extra steps.
BTW, I think Shokar's sealant is very comparible to the look and ease of use of Z2 Pro. It should make for some very interesting comparison tests when it hits the market.