UPDATE: As of 2021, GEO Jobe has transitioned from recommending Admin Tools for ArcGIS to Backup My Org when it comes to migrating items, users, and groups from one organization to another.
Cloning is a very complex and powerful operation that requires some consideration before performing and should not be taken lightly. It is our intent to make absolutely clear, that the cloning workflow is not intended to be a "perfect" one-click solution to your content migration needs, and that there will be times that some items will simply not migrate to the destination. We try to enhance the cloning workflow capability for each update to Admin Tools to handle more scenarios and specific items, but there will be situations where you will need to rebuild items and applications where necessary. The Admin Tools clone operation was not originally intended for comprehensive large-scale migrations and the user is proceeding at their own risk. The original intent of our cloning workflow is to perform much smaller transfers of items that do not require item ownership or sharing to be preserved.
While the clone tools are absolutely invaluable for streamlining the transfer of content from one platform to another, please note that there are many moving parts to this workflow behind the scenes based on many variables related to assorted ArcGIS Content. The best policy for your migration project includes enough time to plan, troubleshoot any unforeseen issues, and accomplish the cloning.
Please note that both the origin and the target platforms (ArcGIS Enterprise or ArcGIS Online Organization) need to have Admin Tools licensed in order to migrate items with the Cloning Workflow.
NOTE: The following resources are ABSOLUTELY CRITICAL to understand BEFORE licensing Admin Tools for the purposes of cloning items: