The Zeta line of books is a heavier version of the Epsilon line. The paper is smooth and white and while the the Epsilon can take light washes, the Zeta can accept a lot more. The paper feels like hot press watercolor paper and I enjoyed painting on this more than I did on Arches (which I did love as well). I'm not the best painter but I had a lot of fun testing out watercolor techniques on here. I'm finding I enjoy smooth paper a bit more for watercolors and I think having a sketchbook of this paper is really exciting.
The Zeta has worked beautifully in the few ways that I've tested it the passed few days. I look forward to getting my own book and having even more art opportunities available to me when I'm out and feel like drawing.