There's a FAQ at the AutoStitch page that notes a few of the specific limitations of the demo version. They also note that a given demo version may expire at some time, in which case one is advised to download the latest version. It may come to pass that at some point in time no functioning demo version will remain available; I know nothing about it other than what I read on their web page.

Note also that they don't sell their own commercial version as such. They license their technology to others, some of whom offer commercial packages based on that technology.

With AutoStitch, I can shoot at will, not telling the camera in advance that I'm collecting images to be stitched in a particular pattern later. I can take them in a relatively complex two-dimensional matrix (5 rows by 8 columns, for example - I don't know how far I'd have to push it before it would have a problem). I point AutoStitch to the files and turn it loose, and it automagically sorts them out and puts them all together.

I have no personal experience with the software that comes with cameras, so I don't how they would compare.