It's simple, UCCE mean single instance and UCCH mean multiple.
multiple instances in UCCE not supported by Cisco. UCCH design support multiple instances and supported by Cisco.
When someone buys UCCE that's understood he need's a single instance, or as an alternative if someone needs multiple UCCE instances that means multiple UCCE not multiple instances. Hope that clarifies.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.