The quantity is impressive. The Daizenshuu collection itself is seven whole books of information and artwork, which is fairly nice. D7 especially is great for its encyclopedia-esque layout.
However, the quality is somewhat lacking overall. Some excerpts sound logical and add to the lore of DB, while other excerpts come out of fucking nowhere (like Tenshinhan's alien ancestry), contradict established concepts/items in the original manga, contradict other excerpts, or just flatout don't make sense and are transparent asspulls just to fill space.
The books are nice to have as reference or to keep things organized as far as the timeline, who battled who, the very broad story strokes, character transformations, etc. But for intricate details, if it doesn't jive with the manga, then it's not valid. If it supports what's in the manga, have at it.
Nobody should be forced to use or neglect the guidebooks if they deem so. But since they are secondary material to the manga—not something with equal say—then they cannot logically trump what's said or done in said manga. They're guidebooks, after all, not rule books. Akira Toriyama's stamp does not mean everything that's officially released is on equal footing with his original vision, nor does it mean it necessarily has to override someone's opinion if evidence is in that person's favor against an excerpt that we can't trace back to either Toriyama or someone who worked closely with him or had his direct input on the matter.
Personally, I find it incredibly asinine to present a guidebook excerpt and expect everyone to automatically bow down to its word, especially if that passage clashes with something from the manga.