I am currently in the biomedical sciences certificate program at USC-SOM Columbia. We just finished our first semester.
I've had interviews and was recently accepted to medical school, but as far as the program goes, they recommend you go through the program and then apply the following cycle. They do save a few spots at USC-Columbia and USC-Greenville for the certificate students during the year you take classes, but the main goal is to get better grades and show that you can handle the workload. The students that went through the program last year said that many in their class had acceptances to USC, USC-Greenville, MUSC, and VCOM-Carolinas.
First semester you are required to take 3 classes: Biochemistry (3 hours), Human Cell/Molecular Bio (3 hours), and either Immunology OR Neuro (3 hours).
Second semester you take 2 classes: Anatomy (3 hours) and Physiology (6 hours)
So far, I feel that it has been worth it. I've gotten to take classes that are taught by many of the med school professors at USC-SOM Columbia, and the faculty are good at giving advice for applications and interviews. I have learned a lot in this program, and they did go way more in depth than undergrad courses. The workload is extensive, but it still isn't full on med school difficulty. It will help you to develop good study habits and to adjust to graduate/medical school more than your peers who just enter med school after undergrad.
If you have any specific questions or want to know anything more, just PM me. I'd be happy to answer.