I noticed that an earlier reviewer indicated that these books are made with "cheap" paper that is not ideal for wet media. I'm not sure that I consider the paper "cheap," but I do acknowledge that some of his criticisms are valid. The paper is extremely thick, stiff and has a great plate surface. Wet media - water color washes - tend to bead on the surface of the paper and washes always dry duller on it than I intend for them to.
That said, as an artist you really need to consider what you want to do with the media before you use it. I'd not recommend these sketchbooks for individuals working in a crumbly media like charcoals or pastels and I wouldn't recommend them to be used with washes. The paper is simply too stiff and smooth - it lacks the tooth to capture dry powdery media and isn't absorbant in the way you'd need for it to be to secure wet media.
They're fantastic, though, for pencil sketching and pen work, and I also like to use thicker paints - acrylics and guaches - on their pages. The thicker nature of the paper really reduces bleed-through on the pages - a feature I love because I like to make use of every side of every page, and for most sketchbooks too much ink will bleed through onto the other side of the page. Because the paper is thick, you can have a pencil drawing on one side and drawing on the other side typically does not force some of the pencil drawing's lines to smear onto the opposite page.
I use pencil, marker, india ink, and pens like UniBalls in these sketchbooks. Wetter pens and inks (like india ink) do tend to sit on the pages for a little while before they dry and smear easily while still drying. It's just something to be aware of - I'm used to it now and really don't mind working on another area of the page while the ink dries.
I think the best thing about these sketchbooks, though, is that they lay perfectly flat when you open them. (There's no stiff binding keeping it from laying flat - instead, the spine is soft bound so that the signatures roll over each other comfortably while opening and closing the book. You'd think such a construction would be weak and ultimately deteriorate, but actually the faux-leather cover is extremely durable, and the books are quite solid.) You don't have to deal with any curve in the binding, and you can make a sketch that spans both pages and it will feel like you're drawing on one.