Installed Service Bus and Workflow Manager Cumulative Updates on all servers.
Left the farm on the App Sever and created a new one using custom settings (had to specify another database name)
The WFE's seemed to be in an inconsistent state: the Workflow Manager UI had 4 options (Create, Create [Custom], Join, and *Leave*). This was weird so I "left" the invalid farm (maybe it thought it had its own?). Then I joined with the new database names.
Originally the URL's were HOSTS entries and are now A Records. (Not sure if possible cause).
Make sure you specify the correct account (I used Farm account - but it wanted to default to install account).
Powershell commands failed with "access denied" but UI worked.