thanks @shackleton
I did find that one and a couple of other discussions referencing each other, like this one:
It is an unresolved thing.
Or, alternatively and quite possibly, plus ready-to-own-it, this exposes my ignorance of the solution if there is one without Human.
On Human:
I can use this for now
However, it must be stated, as rant - and not confused with “I don’t like plug-ins” (Human rocks!) - that:
When the ‘solution’ to PREVIEW A CURVE in rendered view is ‘a plug-in’ we have failed - failed to insist 
'means it’s on a ‘by-need’ basis:
once enough plug-in avoiders dislike it, then curves will be ‘rendered’ in ‘rendered view’
(shhhhhh passionate rhino-defending patrol, I know I haven’t done anything to develop Rhino myself, and I love rhino as well and this isn’t an attack 
)
Best