Well, comparing m43 cameras with full frame is like comparing Phase 645 sensor with FF cameras. M43 cameras are really nice and lightweight but have their own limitations.

All the Leica m43 glass are so called Pana-Leica glass: Panasonic designed and manufactured but Leica rubber stamped. They still are really nice glass, though :)

Disclaimer: used Olympus 4/3 and m43 for reaally long time but the mirrorless full frame gear feels so much better in the closely same sized package.