I typically use watercolor stretched on a board when I paint. If I want something portable I usually choose a watercolor block of a paper (this is a block of sheets where the all the sides of the pages are glued together to keep it flat when you wet it.)
Needless to say, the idea of painting in a sketchbook gave me some pause.
This book is really nice, but it's the paper that counts for serious watercolor techniques, right? So what do we have: The paper is a cold press, rough surface. It holds up well to vigorous erasing. Ink does not bleed through to the other side and it holds a colored pencil line well. The paper does curl, as any watercolor paper will unless it is soaked and stretched flat on a board. I work in very light, multiple washes, going over the same area many times with glazes, on only one side of the paper. It handles that technique very well, and over time the pages will flatten out again as the book covers help to press it back into shape.
The product picture shows the book in the vertical orientation and you might think that it opens like a book, but it doesn't. If you use it this way it's going open like a note pad. If you want the option for double page spreads, turn it to the horizontal orientation. It's an extreme landscape, very wide spreads. Something to consider if layout is important to your finished art.
If you are looking for a quality book that can give you both good paper and a stunning presentation, try this one. I liked it very much. If there is one thing I'd change, it would be a tougher cover, one that resists fingerprints from all the people who want to snatch my sketchbook!