Hey Stoian,
I bought Enthuware for 1Z0-894 OCE Java EE 6 JSP and Servlet Developer Exam. A lot of the exam question where similar with Enthuware mocks (somewhere around 70%) and i appreciate the difficulty levels as being also very similar. I don't remember the precise number of questions about asynchronous processing but there weren't more than 10 and most of the tricks are covered by Nullhaus and Enthuware. I believe that HF2, Enthuware and Nullhaus mocks are just enough to pass this exam on the fly, much better that i did. Just take your time with missed questions and be sure you understand the subject and why you failed (i didn't, that the explanation for my score).
Thanks.