Is the blade offset saved when I power off the M1?

Yes, once a blade offset is saved to the M1, it is automatically stored in the tool until a factory reset or new calibration. The saved blade offset should appear on the screen each time the zero button is clicked.

Sometimes, it may appear that it is not saved if blade offset is "OFF" vs  "00.0."  See this article for additional information on the differences between the two.