Vallejo's metallic paints are really bright as well as shiny. I suggest washing them after applying to a model if you're looking for a more used look. Definitely thin them with an actual medium, not just water because the metallic flakes will break up and cause inconsistencies when painting!
Vallejo's description below:
Highly pigmented, light fast and waterproof once dry, and packaged in a spillproof plastic 17ml bottle with eyedropper.
Vallejo Game Color and Model Color are special selections of water based acrylic colors for players and collectors of miniatures games. A formula particularly designed for abherence on plastics and metals, using a new resin of unequalled durability and resistance to scrapes and abrasions.