I second this. For vehicles I've owned, the aftermarket manuals have been a drag. If I'd buy three of them, I _might_ find the section of the vehicle I need to know about.
I was extremely disappointed with the Popular Mechanics/Alldata disk that I bought for my '92 Ford Aerostar. It covered so many cars on one disk that the diagrams were rendered with such bad resolution as to often be worthless. Just like the books, it was long on general information that I can get anywere, and inadequate for my practical use.
These books have always been disjointed. They typically go into great detail explaining exactly how to rebuild every single engine ever used in the vehicle, as if everyone is just dying to do this. But just try to find how to change a light on your dashboard -- LOL. In general, too, my experience has been that the books, in an effort to keep inventory down, cover too many years and, thus, with inadequate detail.
At one time, I liked Haynes manuals very much. Lately, the ones I've used and looked at have been just like the others.
At the other end of the spectrum, the only way to buy the real shop manual for my Ford product was via a third party. I detest this manner of farming out data (and in electronics, parts) because that third party can be in the business of ripping off the consumer -- in the case of my Ford, the price of the book was $165, and more publications were required in order to work on the electricals.
Richard