I like your plugin. But, the current instructions in the Codex don't correspond with the reality. I did find your revised instructions in another post, so I thought I'd place them here for others' benefit:
1. Edit a page or create and save one. It must at least have a title.
2. In the Custom Sidebar section, check Activate a custom sidebar and select the sidebar to replace. [My note: I just used the default one, "Pages Column".]
3. On the Appearance->Widgets screen, place the widgets on the newly created sidebar that matches your post.
As for the "Settings > Per Page Sidebar page" instruction, that does not view.
As a webmaster for CMS type sites, this sort of plug-in is invaluable. It provides far more layout options for the designer. (If it can do the same to posts, then you've got a fan for life!)
I'll test it out on a few more pages. Then I'll send you a "donation", which no doubt you deserve for putting this together.