Well I have used Whizlabs SCEA exam simulator. I used it to get a feel of real exam, the time I spent on each question, how to review questions once you answer all the questions, etc. After all it is a simulator so it may not have the depth and difficulty level of real exam. I used it for improving my reading practice of questions because sometimes in real exam due to time pressure we do not read questions carefully and we end up in giving wrong answer but with this simulator I could find out my mistakes and I avoided them in real exam.
After all it depends on you how you look at it. Some people may not different opinion about it. Do not 100% rely on it. As I said it is a simulator and not real exam. You need to study through books and other reading material to clear your basics.