I just started using the audio osmosis for the April MCAT, listened to about 5 lecture topics now.
It's Ok, I mean, you shouldn't expect to get a 45 from listening to these guys go over the basic sciences. And that's what this is, they cover the very basic MCAT topics tersely (as stated above), so it is nothing extraordinary by any means.
The strong positive of these CD's is that it definitely mixes up your routine. It is a nice break/reward to sit and listen to the MCAT materials instead of just reading/re-reading and doing questions. And you listen every other day or so, so it's like having some buddies with you helping you along. But it is just a nice optional aside, by no means mandatory or a MUST to have.