Thanks for the info Eck, very helpful!
Being rather dim up top at times, I'm not sure exactly how to read the information on the NSW Weedwise site. Are only the Opuntia/Cylindropuntia/Austrocylindropuntia species specifically listed on Weedwise illegal, or is there a blanket ban in force in NSW? (except O. ficus-indica)
By comparison, the site identifies 3 Harrisia species as regional weeds, but doesn't mention H. jusbertii.