People may not realize by the name of the module "Demonstration Site" that it is an absolute must have for testing and development because it allows easily creating snapshots of the site and being able to restore them. It has been useful for years as a drupal module and was back ported to Backdrop. It works great!
It is different than the backup_migrate module and while sites will continue to have use for the backup_migrate module, the demo module has two significant differences:
1. The demo module saves a database dump and on restore (or as it refers to it, on reset) it drops and rewrites the database, removing any tables that may have been added since the snapshot. This is a behaviour that backup_migrate does not do by default but has an advanced option for it.
2. The demo module, also saves the config files and restores them on reset. This is something that the backup_migrate module does not do.
As a new or experienced user this module is very handy to create snapshots of a site. It can also be used to save a snapshot and then test a new module or even the preview release of Backdrop (you still have to have the original core files in a backup or git).
Yes, it can also be used to create a demonstration site with automatic reset on cron. But, that is a feature that fewer people may need.
To install it go to "Install new module" and search for "Demonstration site" and for more details see https://backdropcms.org/project/demo