And to answer your question, yes, all of the CT's are the same. The M's just have the highest O/S count, so there are more available and being passed around (16 million vs. 8 million for the N's and 12 million each for the L's and K's.).
N's have no market maker still, so those have a limited trading ability. I'm not sure why the trustee hasn't up listed them yet. I sent out a few more emails, haven't heard back yet. To get N's, you may have to bid high to trigger a response. We used to have to do that with all of the CTs before the up listing.