Colour mixing can be a bit challenging trying to get just the right amount of water and pigments floating around on your palette, and I think it would be nice to have a wider range of tubes available. The paints are a bit expensive for the tiny tubes, but I find a little pigment goes a long way. Obviously this medium travels a lot better than oils, and I think I might have just found my new plein-air medium.
Here is a couple of little tests I did, a landscape from a photo I had laying around from Muir Beach and a quick portrait done at a workshop at school.