Although the range of colours in the box isn't great, the water brush is a lot of fun.
Like a lot of other brush pens, the water brush really allows you a lot of freedom of expression. It holds its shape, is easy to control and easy to clean. You can swap between colours in a flash and play about in a way that isn't always easy with as standard brush and water colour set. I actually found myself using the brush interchangeably with Aquash, Winsor Newton inks and Derwent Inktense blocks.
I would recommend getting this set, or one like it, just so you can experiment with the brush.