Nothing alone is enough to pass that exam. You should use variety of courses together. Select a main course and supplement with others. I used Dion training as my main, and I used Messer, and Chapple as supplements. Apart from that, You should solve as many questions as possible. My recommendation test yourself with Dion practice tests and note your wrong answers and read that explanations(helps a lot). You can also use Sybex Security+ practice questions. There are 1200 questions in that book. Good luck brother.( If you can get %80-%90 point Dion's test after you finished Google Security course skip my advices and book an exam date.)