I found that in WordPress multisite, users who are not superadmins did not have access to the settings page, even though they were admins of their own sites.
This was because the plugin checked for the capability edit_plugins to allow access to the settings page.
In includes/Options.php on lines 45 and 76 I changed edit_plugins to activate_plugins and everything worked fine for the admins of individual sites. (In multisite, site admins can activate plugins, but not edit them).
Maybe a future update could make that change so the plugin (which looks like a good one!) would be multisite-friendly?