I am very thankful for CDP. I had been scoring mid to high 20's with Kaplan. Then I ran into CDP. First test, 20. Then in respective order: 20, 18, 21, 23, 22.
I scored a 22 on the real one.
The CDP is pretty much spot on, with the exception of the keyhole. Their shapes are what you have seen everywhere. The real test keyhole is just ever so slightly different (won't explain further), but I think CDP, since you have been practicing on a realistic level, prepares you.
All in all, it is well worth the money. Do the ACE version, 10 tests, practice like you mean it and you will do well. (I took a test every morning for a week, then scaled off to other subjects, then took 3 in a row right before the test)
EVERYTHING you do while you are preparing for the test, make sure you do it under testing conditions.
GL