Until now there are three knowns problems in the beta:
1.- The bucket rendering with Mental Ray doesn't work well. It seems this will require a fix from Autodesk.
2.- The 3D models loaded from the library are visible in the viewport, although they are stored in a hidden layer. This is a Nitrous problem and it should be fixed in the upcoming Max service pack.
3.- Some instability issues with the Library Browser (just reported). Perhaps this problem is related with 2, we still have not reproduced it here.
Personally, i would wait a bit more before using the plugin in production. Also this Max release is internally very different from Max 2012, specially because the migration to Unicode.