Gabe, unfortunately it doesn't work well for me.
When I press the SPACE key it does cause the item to popup, but then it will NOT respond to further keyboard commands, like arrow up/down.
This was noted last year by another user, and while several workarounds were attempted, none seemed to always work. See Popup menu in Prompt for User Input problem.
I don't have this issue with any other popups in any other app on my Mac, so I'm not sure why we do with KM.
@peternlewis, can this be fixed?
BTW, I'm running macOS 10.11.6, so maybe that could be a factor.