In the R22, which is the only helicopter I really know about, there are two reasons for the simultaneous aft cyclic. One is to stop the nose dropping when you lower the lever...can't offhand remember the exact reason why the nose tends to drop, but it does. This just requires slight aft cyclic pressure, to hold it up rather than actually flaring. Slightly more than that to flare will raise the RRPM, and I would say it's absolutely necessary. The reason? On my instructor's course I was given a throttle chop; I was told it would happen, but not exactly when, and told to just lower the lever, not flare. The reason was to show how low the RRPM will drop in the R22 before you can get that lever down. Well, I would have sworn I dumped the lever instantly, but the RRPM was still down to around 90%. Knowing that...I teach lower the lever and flare simultanteously, and that's what I do. Hopefully it'll be instinctive, because in the R22 if the donk stops, it would have to be instinctive to do it fast enough.
