Hi Anthony,
I cannot help on the PMI practice test, as it wasn't available yet when I studied for my PMP exam. So I can only share my experience with the PMPrepCast, which is entirely positive! I found the wording and the way a scenario is described very close to what was in the actual exam, which was terribly reassuring to me!
I would have expected the PMI practice test to be the closest to the real exam, but there are many other students who shared the same experience.
If you felt uncomfortable with the PMI practice test to the point you decided to drop, I would recommend to keep practicing with the PMPrepCast exam simulator, and focus on reviewing the incorrect answers as well as the flagged ones, even when you answered them correctly. This was one of the most useful things for me, and if you found difficult to see/understand the reason behind the correct and wrong (this was particularly helpful for me!) answers, I am not sure I would keep practicing this practice test. Maybe you can just give it another try to go through until the end?
Good luck with your exam,
Gabriella