Let's start with the big one... I've read in multiple places that Unicomp isn't using a true TrackPoint mechanism, but rather a mechanism of their own development, for the pointing stick on the EnduraPro. True or not?
(If that isn't true, and it's a real TrackPoint II in there, then there aren't any true dealbreakers on the EnduraPro...)
Now, next question... I've read in some places that it's possible to call Unicomp and request a black/black model, rather than the black/silver or white/white model available on the Unicomp site. True? I'd prefer an all-black board, and that might sway me to the M13 if I can't get the EnduraPro in black/black. (I've already ordered a white M13 that'll probably end up being used at work.)
In the EnduraPro's favor, it's in the Unicomp SpaceSaver chassis, and it's 104-key (which will make using it with my Mac easier - remapping for 101-key is slightly annoying.) Oh, and built-in USB.