The book is a necessity. The practice tests are rife with errors. I offered to submit errors for compensation or a paid position and apparently they dont care. unfortunately the competition doesn't compare in the amount of material Kaplan provides.
Topscore and Dat Achiever have superior tests as far as accuracy of material goes. Most of Kaplan's tests are similar to the real DAT except when the test has like 3-4 mistakes it is really frusterating.
Example: everyone who has taken the kaplan practice tests online knows about several problems that refer to a figure which will not load....so u automatically get it wrong.
Other problems are missing less information, but still not enough to answer the question. Etc. I wish Kaplan would get their act together. Better yet, I wish princeton review would put up some competition.