no, Polly Scale isn't pre-thinned (neither is Aeromaster Acrylic)
You might be thinking of MisterKit acrylic paint, it is supposed to be ready to airbrush right from the bottle,,,,,,but, it also comes in 1 oz bottles for about the same price as a 1/2 oz bottle of other brands. MisterKit also has that same fine pigment difference as Model Air and LifeColor.
I don't remember if Aeromaster's second Acrylic paint line was thinner than Model Air or not,,,,,,,all the bottles of Color of Eagles I have are now thicker than Model Air (from age)
Rex