I have been using a few of the Xtreme Metal range of colors. I really like them and the finish seems to be very durable, compared to the fragile nature of Alclad II, which I also really like to use. The one difference I have found is that it is not 100% required to prime prior to using these paints. I have used them straight over plastic that has only been prepped by wiping it down with 91% isopropyl alcohol. I have not personnally tried to use weathering washes that are mineral spirit based over them. I have used Tamiya paint thinned with lacquer thinner over the top and done some chipping work
This is done on a current build I'm working on:
As for the base coating. On the above picture, I did apply a base of black Stynylrez before spraying with the Duraluminum from Xtreme Metals. I also have sprayed the engine cowl and cowl flaps in the dark cowling color for A6M5 aircraft, these I did not use the black base on and I felt that I got an even nicer metal finish than I did with the black base. I wil attempt to get some photos of this tonight or tomorrow and add them here.
Personally, Xtreme Metal, though listed as an enamel is pretty potent smelling stuff and highly recommend using a mask and exhaust fan if available or spray in a place with good ventilation. I have not thinned my Xtreme Metal as it is airbrush ready right out of the bottle, just like Alclad II. Light coats in multiple passes makes for brilliant finishes.
I hope that helps you out a bit.
I buy a lot of stuff from Scale Hobbyist as well, and have also been purchasing from Hobbyworld-USA (Matt at HW-USA has been getting most of my business as of late).