Oh, I get it now.
Hmmm, I think the 203 can be set to continuously shoot with mirror up and the 503 mirror has to be manually done each shot. I don't have a 503/CW winder anymore to check that for sure.
So if I'm right, doing a sequence of images for dead-on register the 200 winder may have the advantage in that you wouldn't have to touch the camera. But if you alter a CW winder to work on a 200 camera, then it's not an advantage.
I'm sure I'll be corrected on this if wrong :ROTFL:
BTW, the 200 winder is actually quite nice to use ... the design is such that you hold and shoot the camera as you would with no winder except you hook your thumb into the space between the winder and body. So like with no winder, both hands are holding the camera from below. Works better with a WL finder.
For holding the camera on it's side using a prism finder, I think the CW would be better because of the grip strap.