R4A - It's a rangefinder camera with has the Auto-Exposure settings +A+ mode. When set to the "A" mode, the camera will auto-select a shutter speed that best correspond to the aperture setting with the right light meter reading. Example, on a bright sunny day, if you set your aperture to f5.6, the light meter reads best corresponding shutter speed is 1/250, then the camera will Auto select the shutter speed 1/250 when you press the shutter release.
Since the shutter is electronically controlled, the camera needs battery to work. No battery, no fire.
R4M - Full manual. No Auto-Exposure settings. Does not depend on battery to work. Only needs battery for light meter to work.
Hope I've explained in the most layman term.
Depending on your needs, choose a body that most fits you. The R4M is more for photographers who are more seasoned in manual controls. Not that setting aperture and shutter speed is rocket science, when the photographer is on the move, speed is important, able to set the settings correctly and shoot comfortably with a full manual body, needs some skill.
The R4A is a easier camera to use. If you are not the type who wants to worry too much about settings, just want to capture the moment, at the same time want the flexibility to choose which settings to use (manual over ride), then R4A is for you.
If you are a infrequent shooter, just like to collect camera bodies, just like to feel and hold the camera and only shoot with your D200 or 5D, then the R4M is a better choice. WHY? A full mechanical manual body normally holds better value than a camera with electronic components 30 years down the road.
