Minor update on that blocked extruder I had - I wanted to use the Flashforge to print a model rocket nosecone for a friend so decided to have a better go at unblocking it.
Heated the nozzle up to 220° and tried to reverse the filament out - no good.
Same for 230°, so I ran the nozzle up to 250° .... still no good. So I tried extruding and that seemed to work okay.

So I took a punt and set it up to print the nosecone and it all worked just fine. FWIW I upped the extruder temp to 230° and didn't have any blocking problems.