It looks like these two regulators are exactly the same device. Did
Xantrex repackage the Balmar?

Yes, but not those two.

The Xantrec Model# 84-2006-01 is the same unit as the Balmar MC-512-H
(which is the same as the MC-612 except it has colored LED's instead of
an LCD display).

FWIW the ARS-4 has been replaced by the ARS-5.