I have some, I use it sometimes on brush painting figures. I haven't had much of a problem with the paint drying too rapidly so I've only used it in the airbrush a few times. I didn't see that much difference but again I didn't experiment with it all that much.

It's not that expensive, if you're having issues with paint drying in the brush you might just try different amounts and see if it makes any difference to you.

Sorry, I'm not more help here...

I use it to make my own Acrylic thinner so the retarder is automatically in all the Taniya paint I use.  i think it makes the paint smoother and and doesn't dry in the air brush when you're spraying.

Making your own thinner is way cheaper and I think is better than the store bought Tamiya thinner as well.

here's the formula;

In a 250ml container mix , 2/3 water,  1/3  91% alchohol,  1ml flow retarder,  1ml flow improver

When i'm brush painting I'll add a drop or two in the jar of paint so it flows more smoothly as well.

Do you use specific brands of retarders and improvers ?

I use Liquitex because that's the only brand  i found at Michael's ,my local craft store. I don't suppose it matters but i would keep the brands the same on both products.