The CP16A is very similar to the older Auricon newsreel camera, in fact the CP16 movement is a derivative of the Auricon movement. These non-reflex cameras often use a Som Berthiot or Angenieux "dog leg" zoom lens that works like the optics of a typical super 8 or the Bolex H16 cameras. They use a semi silvered mirror or prism to pass a portion of the image to the viewfinder, resulting in a slight loss of brightness to the gate (2/3 or 1 stop).
The CP16R is a mirrored reflex camera such as the Arri and Aaton cameras. A spinning mirror doubles as the shutter; when the camera is stopped the mirror transfers the image to the viewfinder assembly; when the camera is running you see a flashing image in the viewfinder as the mirrored shutter swings past.
The CP16R went through a few generations of shutter design. If you have a choice you would prefer the later, "half moon" shutter, over the earlier "bow-tie" shutters, as the later cameras are reputed to have a more stable image with less streaking. The two shutters are not interchangable.
I believe all CP16s are crystal sync motor driven. The Auricons mostly used AC synchronous motors to achieve the same end (not all Auricons are sync; the unmodified 100' CineVoice cameras were not), but they then had to be driven from 120VAC house power, wheras CP16s are battery powered.
I've got a "chop top" Auricon conversion that I've rehabbed and it works great, also a CP16R that I paid 5x as much for, but it's dead in the water. Which one should I use?