I think it doesn't work right in MultiSite. I activated the plugin on one site in our MultiSite system, and then found that the Widgets page in the main site was broken. The right-hand portion of the page was gone. I deactivated the plugin on the test site, and then the main site was good again.
For now I can use the plugin Hana Code Insert to do what I need; maybe it's more appropriate for today's project anyway. But I thought I'd mention this because a plugin to allow widgets in page or posts seems like it could be very useful. I'd like to revisit this plugin sometime.