I have to have the Standard 2000i if I intend to run only one unit.
The Companion has to have another 2000i (well, as Honda says), it has to have a companion.
There is so much fiction out there about the eu-series generators! The standard and companion eu2000i is the same darn device except for the outlet configuration. If you read through the companion's Owner's Manual you run across multiple references to running it by itself, including one about what started this thread:
"For single generator operation, the parallel operation cable must be removed".