I find it strange that people are asking others to give them an opinion on how beneficial the NL headrest is when each person's benefit will differ, depend on the amount of shake they have.
As I have mentioned in a previous post, if you have little or no shake there is nothing for the headrest to compensate for so those people are likely to say that it doesn't work.
Then there will be the rest of the people, all with varying amounts of shake and therefore varying degrees of how effective each individual views the headrest benefit. In these cases any two people will to need to have similar amounts of shake in order for them to have a reasonable chance of having the same benefit from the headrest. Unfortunately, I don't know how you can simply measure the shake variation, although there might be a sophisticated way. But until some way found, just asking someone what the benefits of the headrest are in practical terms will, most probably, give you the wrong answer.
Stan