I use a black primer, with a first dry brush of grey and a second very light dry brush of white.
After that only 1 layer of Xpress colors is used and you basicly have the effects shown here. Only the metal is done differently, a medium to to dark metal paint with a Xpress 15/35/50 mixture of yellow, red and water was used here.
All in all I save a lot of time and detailed brushwork.
On the orks it looks magnificent I think, these days I am working on Freebooter's Fate Debonn. These look also very pleasing, but for the faces which got a bit too much of a contrast, but I am working on that issue.