Link backs are not because of the demo. Full one has it too. You should know that right of use third party rss content comes with the obligation of using a link back to main article. Is not really a "law" but common good practice. However, it is all controlled from template (see Post mask) and you can take that read more pard out if you want to.
Does RSSE strip out links from the original content and add my specified Aff link?
No. It would be hard to know what links should strip or keep, as in a feed can be various useful links and maybe not even related with your aff links (as in niche)
Does the demo have any restriction - (3 days - tick tick)
Noother restriction then the 3 days