1. There should be no need to use the word 'about' in pre-flight planning. Exact calculations should be made.
2. The NTR method I have consigned to the trash can of memory. I vaguely recall that an observed angular error was multiplied by the reciprocal of the proportion of track flown since the last known fix, or something like that. Too much hard in the way of hard sums - and excess error from incorrect assessment of observed angular errors.
Why are so many people so seemingly wary of teaching the basics of the whizz-wheel? It's hardly difficult - I learned it at 16!
The idea of planning an IAS to make the TAS 'easy' is a new one on me. OK - on Hunters I used to fly at M0.8 plus or minus the headwind, so it was somewhere between .75 and .85 most times so that 8 miles a minute could be used for rough calcs, but a light aroplane has a very restricted range of IAS. To teach students to set an RPM which would give 96 KIAS is a waste of time - just fly at the correct cruising speed having spent a few minutes with the whizz-wheel prior to flight.