Hi, practically they do the same thing.
Main difference is ofcourse the environment that you can use it on.
Unattended Robot comes with UiPath Orchestrator for Production (Considering it is FLEX skus)
Non Production Robot comes with UiPath Orchestratior Non-Production (Considering it is FLEX skus)
Non Production Robot does not have access to data service whereas Unattended Robot has access to it.
Do note that the the Non Production Robot is now called as UiPath - Flex - Unattended Robot - Non Production