I just spent the day shooting exclusively with the ZM and a 21 / 35 combo. I like the experience, and it's slowly becoming second nature to adjust my eye to bring back the RF patch in the VF --either that, or I'm becoming more tolerant of the flaw.
The one thing that stuck out was how much better the ZM is as a Manual metering camera than AE. In AE, I kept wishing it had the AE-lock system of the M7 and many other cameras: half-press lock, and recompose. I much prefer that approach to exposure compensation or reaching for the button centered at the back of the ZM. I even prefer the AE lock of the Contax G.
In Manual mode, the fact that the meter readout is tucked away on the left side of the VF becomes a tremendous assets for those who, like me, prefer an uncluttered VF. I peek to the left, adjust exposure, and then shoot away happily without ever paying attention to the meter unless the light changes.
In AE mode, the hard to see readout is a hindrance because with AE it's mandatory to keep an eye on what the camera decides it's the optimal exposure...did the lamp in the back skew the reading too much? how about the metallic reflection from the coffee table? etc. Trying to test the AE mode, I found myself shooting at speeds twice as high from my initial guide reading off the palm of my hand +1 stop. I probably fired off three shots before realizing something in the frame was tricking the AE.
Still, since I prefer manual metering, I like that the ZM is very discreet in this respect, and the single 50mm and 35mm framelines, are a luxury that only M2 owners can share.
One other consideration about built in meters, since I'm also trying to decide between internal or external... don't you find that you can be a lot faster with external meters because your camera can be set and ready to go without even raising it to your eye?