I am not doing a formal program, but I looked into it and this is why I decided against it.
As far as I know, the certificate is very meaningless. Also, a friend of mind, who somehow took one class with the formal post-bacs over the summer, said that they were all rich brats from private schools with useless BA's who would dominate the class and ask irrelevant tangential or philosophical questions instead of focusing on learning the material for what would be on the test. If she hadn't already taken a handful of more advanced chem classes, and was only taking this for a requirement, she said she would have really been disadvantaged by the lectures.
When I went to ask about the formal program, I was surprised that the student working in the office had actually transferred out of it! She said it was actually tough at first, but the main thing is just finding other post-bacs in the general classes for studying with.
One thing is that I've heard it's very hard to get volunteer or clinical experience in San Francisco, and one big selling point of the formal program is that they have connections. So if you are worried about that, especially if you have little experience to begin with, then maybe the formal program will help. However, if you are confident about getting or already involved in clinical extra curricular's then you might not need the help. Or, I've heard it's very easy to get experience if you are able to travel to the East Bay or places outside of the main clinics in SF.