I can't have an opinion on the handling quality of Holbein watercolours as they are not available locally and are very expensive to import them. But the fact that their binder separates from the pigment is not a good sign. If it separates on the tube or in a blob of colour placed on a palette, it will separate in time on the painting, making the pigment fade as the particles of the paint pigment will start unstick from the surface of the paper.
The binder is there to hold the pigment together and stick it on the surface of the sizing of the paper, that in its turn is there to regulate the absorbency of the paper.