I was skeptical about using the Therapist Development Center because I heard that it was "easier" than AATBS. I used AATBS material exclusively until I failed the Clinical Vignette exam. I decided to give TDC a try. The program indeed prepared me to approach the exam from the perspective needed to pass. To pass the exam, one needs to be very clear on what is being tested, and for that, having the right strategies is absolutely crucial. The material offered by TDC fits that purpose exceptionally well.
The fact that it is concise and straightforward is definitely an advantage too. I found all of the aspects of the material helpful: framing, crossing the clearly incorrect answer choices, being clear on the difference between legal and ethical obligations, and many other relevant elements that indeed appeared on the real test. I completed the exam with 20 minutes to spare, just like I did on the practice tests. This is different from the first time I took the test, when I spent way too much time reading and rereading the vignettes and rating the same elements multiple times. The strategies presented in TDC material have eliminated the pressure of time for me on this exam (and I am not a native English-speaker). Bottom line, I highly recommend giving TDC a try as the primary preparation material of choice.