I tried to import the Offline Bundle for 5.x of the fling version 1.23 (file name esxui-offline-bundle-5.x-6360286.zip) into Update Manager (I'm using the vCSA 6.5 U1) and that failed with the following error:
Failed to upload the file.com.vmware.vim.vmomi.core.exception.UnmarshallException: Missing value for non-optional field updates
Please fix that in the next release, thanks!
... in addition I noticed this: After manually installing esx-ui version 1.23 I can no longer use Update Manager to scan or remediate the host, because "esxupdate ... returns error 99".
So there is something seriously wrong with this package :-(