Basically, you need this book.
Some of the drawings contained within can be found in the Fantagraphics Sketchbooks nos. 1-5.
But many of the drawings are not included in the Fantagraphics books (which is why you need this).
The new volume is far more affordable than the outrageously-priced box set.
We still have not seen the Zweitausendeins Sketchbooks so we do not know what kind of duplication there is.
From Taschen's own website:
"It’s the old story. When TASCHEN released the first limited edition of Crumb Sketchbooks 1982–2011, fans drooled over the gorgeous packaging of this six-volume boxed set, the artist’s thoughtful editing, the hand-written introduction, marbleized page edges, and signed Crumb-colored art print. Not all, however, could afford the steep price. So they whined and coveted, with the wail growing louder when the second boxed set, 1964–1982, was released the next year.
Covet no more. Robert Crumb. Sketchbook, Vol. 1: June 1964 – Sept. 1968 combines the two earliest volumes from the limited editions, produced directly from the original artworks now belonging to an ardent French collector, into one fat 440-page Crumb feast, selling for an irresistible price.
This book contains hundreds of sketches, including early color drawings from the master of underground comic art, cover roughs for the legendary Zap and Head comics, the original Keep On Truckin’ sketches, the first appearance of Mr. Natural, plus his evolution and refinement, Fritz The Cat, the Old Pooperoo, and many, many voluptuous Crumb girls, all wrapped up in a quality hard cover featuring an illustration newly hand-colored by Crumb himself."