I would like to borrow one but the only photographers I know well either shoot Canon or don't own an ultra wide unfortunately.
As for stitching photos together I've tried it and you're right it's not difficult but I don't feel it suits my way of working. I also imagine you won't get that same perspective that an ultra wide can give you.
For anyone else who has a similar choice to make I found this video interesting for considering the 3rd party options, just ignore the 2 canon lenses at the start, first 3rd party lens review starts at 5:40
https://www.youtube.com/watch?v=VRSyTOosOcc This is just one mans opinion and I wouldn't base my decision on it alone but I found it a helpful starting point. His channel also has more in depth reviews of each lens which are informative if you can get past his slightly odd way of talking.
Tokina 11-16mm is still my favourite as it possibly has better IQ than the sigma 10-20mm but I think I would be happy with either.