What are the differences between MPFB1 and MPFB2?
There is quite a huge difference.
MPFB 1 was a blender addon which largely implemented online import functionality from MakeHuman. It was not able to operate standalone. While it did have some extras, the main focus was importing from MakeHuman.
MPFB 2 is a full character generator on its own. It does not need MakeHuman to operate. It aims to implement all the functionality necessary to model humans directly in blender. While MPFB2 also implements the online import functionality for MakeHuman, this is now only a small part of what it does.