Hi SEBLODers,
Thanks for your great question.
So a free object can be used to take the hand to another simple "object" from another extension or application. A free object is used in relation with the free storage.
By using it you will be able to manage this data in a SEBLOD view (form view and search/list view, be care SEBLOD has no content detail view at this time and used the Joomla article view which can not be used here).
You know "Article", "Category", "User", "User Group" objects which are native into SEBLOD.
Theses objects require a specific SEBLOD Object plugin because there are complex objects with a lot of different interaction between database tables.
The free object don't require some custom development (such as a object plugin) but it's working for SIMPLE object. That means an object which depends only from one database table.
Example, on VirtueMart the "product" object is complex because different tables are used and it calls itself some other object such as images. So it will required to develop at least 2 object plugins, one for product and another one for image.
Another example, by using the free object you can display item from Joomla menus in a SEBLOD list such as here http://demo.seblod.com/seblod-addons
So yes, it can be used for a comment system.
Be care the delete function is missing for the free object and we need to add it (written "//TO DO" in the source code).
You can always just unpublish/hide an item by adding a parameter and filter by it your list.
Thanks.