Is there any difference between the ST-E3-NR and the ST-E3-RT transmitters? Or are they both the same?
Probably not as far as functionality goes. The only place I can even find a reference to the ST-E3-NR is on web pages based in Germany. Since these are devices that use radio frequency transmissions to communicate with the same compatible flash (the Canon 600EX-RT), the regulations in Germany concerning devices using certain frequencies may be different and necessitate a slightly different version to comply with those requirements. Even the photo for the ST-E3-NR at amazon.de is of the ST-E3-RT.