What is the difference between them?
I'm familiar with 154CM. I've never owned a knife with a blade made of CPM-154. I have to believe it's similar to 154CM, or Crucible would have named it differently. It seems safe to assume that with a nearly identical name, the steel must be very, very similar, as well. I'm guessing CPM-154 has only some small improvement over 154CM.
Roughly the same chemical composition, but formulated using a powdered metal process. And yes, it makes a huge difference.