Here's the rundown on Bar/Bri and PMBR. Bar/Bri is an institution. They have a streamlined process for taking you from BAR prep to BAR success. Their process is time consuming (most people do not stick to the homework schedule Bar/Bri sets out for its students). Bar/Bri also works hard to add some humor to the process by hiring fairly entertaining lecturers and constantly bolstering your confidence with success stories of seemingly clueless students. Bar/Bri teaches you to look at the exam primarily as a lesson in patience and time management rather than knowledge, and helps you to prioritize all the important topic areas. For these reasons, Bar/Bri is a must. It allows you to focus on memorization and practice rather than on the study schedule planning and outlining that you otherwise wouldn't have time for.
PMBR on the other hand, tests your knowledge of the law. PMBR employs the "learning by doing" method, which entails you complete an incredibly difficult multiple choice question, then go back, read about all the rules tested in the question, learn from your almost inevitable mistake, and move on. The point of PMBR practice tests is not to do well, but to learn from them. This process is not completely necessary and can be quite frustrating at times. Panicky bar preppers are left wondering how poorly they are going to do on the Bar. As a prelude to BArBRI, PMBR is useful to get the student's mind geared to the bar. But as a last week before the bar study guide, PMBR is neither particularly useful nor confidence-building.
I would suggest getting your hands on a PMBR book to go over on your own during the week between graduation and Bar/Bri. I would suggest taking Bar/Bri. I would suggest skipping the final PMBR multiple choice session all together.