Giving Numbers is all well and good. But you end up with FO's who can not adapt with non standard situations!
If your fast (Trend arrow or not) reduce power, if slow more power!!!
I agree setting 60% ish does work on straight in vectored ILS approaches, but you need a bit more Pilot Skill then that!!!
I remember an old instructor friend of mine who taught circuits by, turn left at that house, downwind at the river , then set 1700 Rpm and then , turn at the ..........
All well and good at that airfield, but his students could not cope at any other location.
Where as if he taught by reference to the Runway, well that would be a thing!!
Its a often under used instrument, this window thing!!!