Hello Stefan!
I probably paint metal in the easiest way. I use black, blue and white oil paint. See photo. For me, the brand on the paint does not matter. I always primer my figures with Humbrol. Then I paint thin glazes on a dry surface. I always let the paint dry overnight before I paint the next coat with paint. If you want to paint a little more advanced, you can also use a mixture with a little yellow or brown.