2. Is the M7 running with Android? How can I navigate to previous page when there's no virtual keys on the screen?

A: The M7 is running with a highly-customized Android 7.0 system. You can always use the return button "<" at the upper left of the screen to navigate to previous page. And meanwhile the M7 supports gestures:
a) swipe up from the bottom-left area of the screen to return to previous menu;
b) swipe up from the bottom-right area of the screen to return to home menu.