I did a bit of reading about them (they seem to be popular in other miniature hobbies) and then ordered up a bunch of colors I thought would be horse-appropriate.
Not having any bodies ready for painting, I put out a plea for prepped bodies I could try these paints out on, at a reduced cost. I painted two at that time - a chestnut and a dappled gray.
Tamiya paints put down color fast. That was the first thing I noticed about them. Even when thinned down, color build-up is very quick. Great if you are in a hurry to get a model painted.
I have mostly used "normal" acrylic paints when airbrushing models, paints that you can thin with water, like artist acrylics and airbrush paints such as Golden Fluid Acrylics, Golden High Flow, Com-Art, etc. With those, I can get lovely watercolor effects to build up color slowly, giving me rich, glowing color with soft gradients. But with the Tamiyas, the watercolor effect is much more difficult to achieve. The paints must be thinned way down and when you do that, the paint doesn't adhere well to the model - it sits on top as a layer of paint dust. Using the proprietary thinner might help, but that would be very expensive since I like to thin my paints a lot. And since the watercolor effect is little to none, I had to rethink my way of mixing colors and approach painting in a different way.
Tamiya paints, when airbrushed, go on what I call a "dusty flat". The photo below illustrates this:
Because the paints are SO flat, sealing them with a flat sealer doesn't work (at least for me, it doesn't). I found that Krylon Matte Finish, the bane of many a model horse artist, works the best to meld all the layers and it deepens and enriches the color.
Compared to the paints I am used to using, the Tamiyas go on a lot more grainy, even when thinned. Yes, regular acrylic paints and even airbrush paints can go on grainy IF you spray them without thinning them much. But if you do thin them, they can go on with little to no grain at all, especially if you use airbrush paints like Golden High Flow and Createx Wicked Detail colors. Their pigments are ground super fine for airbrushing so they go on with little to no graininess.
Since the Tamiya acrylics are geared toward military modellers, they come in a lot of military colors - Nato Brown, Hull Red, Desert Yellow. They also come in basic colors like red, green, yellow, white, and black. So with a little know-how and knowledge of color theory, you can mix yourself a whole bunch of horsey colors. But it would be nicer (and easier) if they came in "normal" artist colors like burnt umber, raw sienna and the like.
After working with the Tamiya paints for awhile now, I have to say that I still prefer my airbrush acrylics, even though it takes a heckuva lot longer to build up colors and complete a model with those. I prefer the depth of color and the soft color changes. If I need to build a solid base color up fast, then I wouldn't hesitate to use the Tamiya paints. But for the rest, I would prefer to use my airbrush paints.
One color of the Tamiya paints I really like is the white, just because it covers quickly. When I messed up the rump of a model I was painting (using my normal paints), I used the Tamiya white to quickly cover the area so I could repaint the whole section.