Hello- before I write this post, I'd like to mention that I am, in no way, affiliated with PM Prepcast or have any commercial agreement with them.
I've had an amazing experience with the PMP and ACP exam simulators. I achieved my PMP in Aug last year and my ACP last week. Both the exam simulators provide a very realistic experience of the tests, in terms of language, grammar, difficulty and content. For both the exams, i'd say the simulators contributed more than 50% to my success.
Thanks to the Prepcast team for building such an awesome product!