This service does not collect or store any data related on the users or tenans where it has been used. When provisioning happens, you are required to consent the application with the needed permissions. Those permissions are then used to provisioning the selected template to your tenant.
Customizations and code included in the templates are provided as is. If template is published as a open-source template (like SharePoint Starter Kit), you can access the provided source code from the specfic GitHub repositories.
Microsoft cannot be hold responsible of possible issues caused by a conflict with the templates and your tenant. Please do test the templates in non-production environment and carefully consider if you want to use this service in your production tenant or not.