ADR Seeker, welcome to the forum.
Please tell us more about yourself... are you a patient looking for solutions?
The M6 and NeoDisc are interesting designs. As with all of the devices, features and differences from one to the next.... all come with advantages and disadvantages. So much of what is said about them and what we initially understand, is marketing spin. It's difficult to separate the important issues from the spin.
I wish I could write more about these devices now. I originally wrote about the M6 from SAS-7 in Berlin. See here:
Mark's SAS7 Blog.
Interestingly enough, migration is one of the problems with Neo Disc because the jacket is so flexible and what keeps the core in place is the jacket. It is a beautiful design and is so simple and somewhat smaller invasive procedure. (This may also be something of the marketing spin more than important data because the important work in a disc replacement surgery has to do with getting behind the vertebral bodies to remove osteophytes and decompress the neural structures.)
There is so much more to say... but I have to run.
Again... Welcome!