From speaking with students that I've met casually from BU, they've told me they think the APEX program is just "a way to get the normal stream dental students out the BU facilities, so that they can get in their international students." They said it was a way for BU to make more money.
It was sorta my feeling that the APEX program was something I could've done before dental school, on my own. It sounded pretty much like shadowing. I personally wouldn't want to spend time doing that - but it may be beneficial for some people.
But these are my personal experiences and what I've heard. I don't go to BU, so take what I say with a grain of salt. In general, I think BU is an awesome school, and I'm sad that it gets put down so much on SDN.