Even before finally trying my SA on my M9 a couple of weeks ago, I knew it was going to be a lesson in futility. It has the wrong mount for 6 bit coding as one of the other Leica 21 mm lenses. I chose the WATE from the camera menu and the results were still marginal.
In addition to the overall strong magenta vignetting / light falloff, high contrast edges also tend to show a visible red edge. Obviously this for color files. Even with B&W files the light falloff is much more severe than on a film camera where I find it pleasing and part of the essential signature of the SA. Even with the WATE correction from the camera, more aggressive action is essential in post.
Corner fix can be use to control the falloff for both color and B&W files. The red edge demands a more creative approach and must be applied to individual files. Too much time and effort, IMHO, when more user friendly lenses are out there.
As I mentioned previously, I have the 21mm Elmarit ASPH which I like on the M9 and the CV Ultron 21/1.8 which I also like. Lately I have been using my CV 35/1.2 so my 21/1.8 is in my bag. When I head out with my 35 Summicron, my 21mm Elmarit ASPH goes in the bag.
The Super Angulon now stays on a M6.