Open Acrylic paints are more watery than Heavy body acrylic paints.

Compared to other type of acrylics, they are slightly more transparent. For example, Open Cadmium Yellow is semi-opaque not opaque in the product description. But, it's still Cadmium, much much better than other miniature yellow paints in a sense that you can very evenly apply the paint in a white surface.

It's worth to read Golden's tech info for Open Acrylic.

Cadmium Yellow Medium - Very Good, somewhat transparent than oil counter part, but still good on plastic surface.

Cadmium Red Medium - Very Good, somewhat transparent than oil counter part, but still good on plastic surface.

Chromium Oxide Green - Very Good. Completely opaque, and can be spread easily.

Pyrrole Orange - Very Good. Bright orange, semi-opaque, but looks like can cover most even bright surface.

Phthalo Blue (Green Shade) - Very good. Transparent, no streak.

Phthalo Green (Yellow Shade) - Very good. Transparent, no streak.

Red Oxide - Very Good. Completely Opaque. Since Burnt Umber was disappointing, I'll probably use this for general brownish color.

Payne's Gray - Very good. no streak. Semi-opaque.

Cobalt Blue - Good. Average, it's streaky, but that's expected as I experienced similar problem on the oil counter part.

Hansa Yellow Light - Good. It's transparent, but tend not to leave streak with proper brush control. Since it's transparent, it's best usage is glazing or tinting, or to mix with other colors.

Quinacridone Magenta - Good. Transparent, tend not to leave streak with proper brush control. Can be used for glazing or a filter.

Titanium White - Good. no streak. Semi-opaque.

Burnt Umber - Bad, it's streaky, almost impossible to paint the surface evenly. Blended mixture also has this problem. Either I should use this as wash or very small amount to shade other paints.

Carbon Black - Good, no streak, opaque.

The main benefit to use Golden Acrylic paints is that you can achieve smooth blending fast like oil paints using wet blending technique. For other purpose, you can still use your own miniature paints and washes.

Since you can achieve blending using layering or glazing with miniature paints and washes, there is no point to buy transparent Golden Acrylic paints (with few exceptions).

There is no good opaque yellow paints (without streak) in miniature paints. This is expected. As far as I know, there is no opaque yellow pigment that is non-toxic. Hansa Yellow is transparent, and Benzimidazolone Yellow is also semi-transparent. Since there is no miniature paint vendor that disclose the pigment information, I don't know which pigment is most used in miniature paints. I can only speculate that Hansa is the choice as it is used for the alternative to Cadmium Yellow in artist industry, and it is CHEAP. As far as I know, this can be easily overcome by using Cadmium based yellow paints. If you're a miniature painter who never tried artists paint products, I highly recommend to start with Cadmium yellow. Pick Cadmium Yellow Medium.

For blending with red, you'll need at least one red. I recommend Cadmium Red Yellow here.

It's not easy to mix chromatic orange using Cadmium Yellow and Red, so select either Cadmium Orange or Pyrrole Orange. Note that Pyrrole Orange is semi-opaque.

For green, the only opaque pigment is Chromium Oxide, which is somewhat dull green. Select this one. It's not versatile when mixing with other colors, but as a miniature painter, you'll have a plenty of opportunity to use this without mixing such as Orcish or Goblin flesh.

If possible, select Phthalo Green and Phthalo Blue as well. These are transparent, so they're not a good choice for the base color, but you can mix these with other colors. These have overpowering tinting strength. Some regular canvas painters don't like overpowering pigments, but they have their own purpose. Since there is no chromatic opaque green paint and there is no opaque blue paints, you can mix these Phthalo paints with opaque Titanium white to achieve opaqueness. Due to the overpowering tinting strength, you probably need only a small amount of Phthalo paints, give more room for Titanium White which gives you the opaqueness. Also mixing all three paints gives you very good Turquoise color for verdigris effect.

For tinting and shade, select Titanium White and Carbon Black. These are nothing special, but better to have them as mixing regular acrylic paints changes the drying time.

You may want to add Open Acrylic specialized medium such as Open Thinner or Open Acrylic Gel. You can use Open Thinner instead of water which helps to keep the long drying time. If you already have acrylic retarder, perhaps this could be optional. There is good article in Golden regarding these medium; Open Thinner and Open Acrylic Gel