passed at score 869.
i would say it is not easy, it is not an exam for the concepts , it is not only for when to use a particular service , it is for a specific scenario, which service is the best to use.
not even one question from the whizlab exam, but whizlab questions can help you to learn deeper of each services from the explanation it provides.
i personally read faqs from https://aws.amazon.com/faqs/ twice for the major service topics, in the real test, i still found it is not enough,whitepaper may be the best, but i did read it.
OAI, ElastciCache,read more about them.