We mostly use Frogjuice, it is easy to apply and gives the color a nice pop, and it's "glossy". If it's not available over there there are other products like Clear shield that are similar.
If we need to apply a vinyl film we do it by hand. For the amount of times we need to do it it works fine.
We use it on them all the time. Just did a bunch of diamondplate vinyl with it.Any issues using this on shiny gold and silver print?