John,
If you are having good results with the Polly Scale then I would continue using it and maybe even trying Model Master Acryl and Tamiya acrylics to see how they work.
The Golden's colors are great but I don't know how they perform on plastic.
Most people I know that use them are using them on automotive surfaces or textiles such as T-shirts and denim jackets.
There is a lot of info on their web site on using them and maybe you could send them an email to see what they say about your application.
http://www.goldenpaints.com/
Mike
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon