I have used the dust colours and find they work well.
I use them as a wash - put down some water over the area to be worked then apply the dust in a wash over this. As it starts to dry you can work into it with a wet brush to soften any areas that are too intense and also build up the layers to add more intensity. It is quite flexible and well worth experimenting with.
I used them on my Merkava 4 they give quite a yellowy dust effect.