WP User Terms
Permissions Management. Really easy!
With WP User Terms you can share categories (and all other taxonomies, like product categories, as well) with your users.
So simply set a category to be restricted and and assign users to them too. Now only these users have access to the content of this category.
No more parallel user libraries, no more superfluous roles on top. Because you knew all the time: roles are not made for that.