The Sakura Koi Watercolor Sketchbox is the first set of watercolors I ever bought and it is still one of my favorites. It has a sturdy and cute little design with good quality. The paint is smooth and doesn't dry chalky. All of the colors are deep, rich, and highly pigmented. The burnt sienna and Chinese black are especially pigmented and most times I use lots of water with them.
There is a mixing tray that clips onto the side of the box in three different ways and a little ring on the bottom to hold the box in one hand like you would a wooden palette.
It also includes a water brush,,approximately size 8. Fill the removable vessel with water, attach it to the brush and squeeze for water to wet the bristle and paint from there. The idea of a waterbrush is awesome but I find the base difficult to squeeze so for me I just dip the brush in water. I have read that some people will fill the little wells on the side of the box with water so they don't need an extra cup.
I love the Koi sketchbook, it's relatively affordable, the paint is good quality, and it's compact. The biggest downside is that the watercolor cakes are small so they don't do well with large brushes.