I used Enthuware in my preparation for EJB3.0/JPA1.0 exam. It is a good simulator with questions a little bit more difficult than the real exam. In mock tests I obtained between 80% and 90% scores. In real exam I had 95%. Anyway, probably I would have passed the exam without it, but definitely it helped me to improve the score. I didn't buy Whizlabs because they had some free questions on their site and I found wrong answers even in these. I remember something about the mandatory/non-mandatory ejb-jar.xml descriptor. I suspect they got that question from ejb2.1 (where the descriptor was mandatory) mock test and put it in ejb 3.0 mock without checking.