I haven't used both sealants but I've used both QD. I'd say use whatever QD with your sealant choice, neither adds extra protection or softness. These two QD are mainly for smudge, light dust removal, to help with residue removal. They both are good products and both smell great but Z6 has the added benifit of being concentrated. I would say the price of UPP has been steadily going up. It was 14.95 and seamed to go up to 19.95 overnight, unless I'm mistaken. I'd wait until they have a sale on it, and they often do, if that's what you chose. With the new Z2 I would say it would be hard to find something wetter, maybe as equally wet, but the new z2 is wet as a good nuba. I would like to see a fair comparison of Z2 and UPP for durabilty over long term. Two coats of each on the same panels, and maybe even one on each half of the hood.