I have the same RB67 you do (the original, not Pro-S or Pro-SD) and am very pleased with it. I prefer a lens shutter to camera body shutter because flash sync is available at all speeds. I also appreciate the fact that the camera is all-mechanical. No worrying about dead batteries (except in my handheld meter, I guess)!
Make a habit out of winding the film back as soon as you take a shot. There is no interlock to prevent accidental double exposures in the original model.
The RB67 Pro-SD manual is available for download in PDF format from mamiya.com. There are very few differences in the various RB67 models. You'll notice that you lack focus lock, double exposure prevention, and a couple other misc features.
Enjoy your new camera!