I hate Testor's. Over priced oil based paint that mixes poorly, thins unevenly and reeks like the wrong end of a gasoline refinery has no place in my workshop. I find their products to be extremely inconsistent ever since the resorted to overseas manufacturing years ago.
You can get superior paints for significantly less via eBay or Amazon. Unless I need a high gloss automotive finish, I always use artists acrylics (see my Vermithrax thread for details). For Automotive models requiring a showroom finish, I buy actual automotive paint and primer at the hardware store down the block, or use the automotive touch up spray cans available at the car parts store a few blocks away.
I do swear by Krylon Industrial primers however. Their Matte Black, Dark Grey, Light Lrey, white and Machine Grey get used with such frequency around here I buy a case of each from McMaster-Carr or MSC depending on who has the better price that year. Those primers are so darned good, they can be used as matte finish paint. Those products are worth every single penny and can be used on everything from hollow vinyl and resin, to wood, metal and glass. If you use any solvent based primer on any type of plastic, always allow at least a week curing time.
As a last note, don't waste your time on water based primers. I find them to be useless unless you are working in wood.