Capt on Heat.
Going below 500 agl on FLWOP really has nothing to do with the instructor being concerned about Joe Public, it is actually their concern about the goons at CAA who tried prosceuting a couple of instructors in 2004.
I know of 3 instances where they pulled the radar plots and the instructors had alot of talking to do to keep the enforcement guys off their backs.
Hence the confusion and reluctance - however if i was ever confronted about it I know exactly what page of Part 91 i'll be waving about!
6080ft