Can we please just draw a line under this ridiculous notion that Flex/Assumed Temp thrust reduction is in some way unsafe.
Facts.
It reduces engine wear through lower EGT
It reduces the chances of VMCG problems
It allows far smoother climb out, imagine using full rated thrust in a very lightly loaded 757 with a 400oft level off SID, not fun for anyone
Oddly reduced thrust actually can help in an engine out situation, things happen slower and there is less chance of having control difficulties, plus you still have the protection by virtue of perf calcs that you will make all necessary performance criteria.
So can the idiot SLF who are prattling on about this please stop it.
If you put incorrect performance figures into the FMC and have incorrect speeds then yes, you are in a bit of trouble, but you could just as easily use full rated thrust and have some lunatic pop the speedbrake, retract flaps etc. That will kill you as well.......
As for the V1 > Vr argument, well words fail me. By definition it cannot be, fact.