Every once in a while, I end up having to use metallic paints. All the Ultramarine stuff I did in the case of this army required metallic paints to match what had already been done by another painter. It is definitely not my preferred medium, but every so often, it does provide some interesting perspective on my usual NMM style.
Since the lightest metallic paints are a dingy gray, that can wreak some havoc with the usual contrasts that I look for in my painting. I only found this out recently, during another metallic experiment. I had it on my white paper palette, and I was shocked at how dark it appeared! I guess it is all about the light refractions to give it the lighter appearance.