Magnepan has a trade-up program. You would have a year to trade up to the MG12 if you aren't satisfied with the MMG. Check the Magnepan site for info on trade up options.
Aaronr...For Maggies I would stick with new. They are a unique technology and not easily evaluated as to condition. But if you can, listen to MG1.6 along with the 1.2 and then you decide. Whenever I have bought equipment that was not really what I wanted I have become dissatisfied after a few years, and ended up buying again. When I bite the bullet, and buy what I really like I am satisfied for a decade, and in the end it costs less.