Hi,
Boeing says that ARM mode is normally not recommended because its functions can be confusing. As many of us here I think that after a "few" hours on type these functions are not so confusing after all, but that is what the manufacturer states indeed. If you get into troubles during an approach with A/T ARM and speed off it will be difficult to prove that this was the best solution at that time. In CAT I for me it is A/P off, A/T off. In case of G/A the PM will adjust the N1 value, exactly as it happens in the SIM (or should happen
).
Bye !