Is it better wet or dry?
Both ways work. Wet application is quicker and more convenient and helps the product spread more easily; dry application gives a more controlled and consistent dose to the panel and perhaps has the edge in ultimate performance.
How long does the sealant last?
Depends on conditions and care, but 2-4 months on a daily driver - maybe more if the panel is well-prepped and the product is layered.
Does it layer over other protection?
Yes, it works well as a top-up layer over existing sealants or waxes - be wary of sealing dirt in, but being water-based means that Future Armour won't strip or interfere with mature coatings.
I've made a mess of application, what can I do?
Future Armour can be removed soon after application with a strong panelwipe/solvent like Dodo Juice Stripp-Ex; if it has fully cured then it will need to be abraded/polished off. Use clay, followed by polishing by hand (Lime Prime etc) then tackle by machine with more aggressive polishing techniques if required. Remember, any defects you see are optical and on top of the paint. Your paint is fine underneath.