Some time ago, someone on a different forum recommended photostitching rather than using an UWA lens. I have the Sigma 10-20 and thoroughly enjoy this for many uses especially wide landscapes. But thought I'd give the photo stitching a try with the M-50 f/1.7, and must say, very happy with the result. Stitched in Hugin from 4 landscape shots in quick succession.
IMHO, this technique with a good lens can produce very impressive results without the considerable cost of a good UWA lens.
Obviously, not everything will be possible with this method...Note the occasional dislocated waves...!