It seems to be fine without primer. The pearls and opaques require no basecoat...the red Merc above was shot over black primer. The one below is a combination of pearl copper, pearl gold, and opaque peach shot right over bare plastic. The peach ended up being a lot more opaque that I expected, and kinda ruined the look I was after.
I concur with Tom. These are absolutely beautiful Lots of pigment, covers well, beautiful colors. Very easy to spray. I used a Badger 200 at about 16 to 18 psi. The absolute best thing I've found is that if you have screw up, you can feather it out with wet or dry, and just respray that area. Just like a 1:1 it blends perfectly, no need to respray the entire body, or even an entire panel. It dries satin, so it needs clear. I've used the Aztec clear and its wonderful. I dries rock hard and polishes up great. Here's a couple pics: This is the pearl red with Aztec clear. No wetsanding, just a good polish with "Ultimate Restore" a polish made for slot cars.
And here's some messing around on my part. This is how it looks without clear. This paint goes on real smooth.