Anyway. My daughter has a ridiculous set of sensory issues which I manage mostly by avoiding, cross my fingers and hoping she will outgrow and, in a pinch, negotiating with her. For years, her schools (preschool, kindergarten, even first grade) have attempted to play "beauty shop" with her to get her to let them comb or brush her hair. No one has succeeded. I've tried. My sister -- who has mad skills in this area -- has tried. Sometimes my daughter will gut it out for a while, but she's never okay with it. The topic came up at the neurologist visit, and the neurologist suggested a Mason Pearson brush.
I was like, I have one, I can't imagine it'll be any different but okay, I'll give it a try. I suspect, in fact, I tried it long, long ago, but I sure hadn't tried it recently. So after a few days in a row of trying a variety of other no tears brushes, asking her to brush it, using my fingers, using various wide toothed combs, etc., I broke out the Mason Pearson and she was Completely Okay with it.
It's still insanely expensive. However, if you have a child with significant scalp sensitivity, maybe you have a friend who will loan you theirs to try on your kid to see if it will make a difference. The thought of forking out that much money on a long shot makes me shudder -- and I can well afford the brush these days, but plenty of parents of kids' with sensory issues can't.
It's one data point, anyway.
ETA: The KnotGenie is actually really good at dealing with knots, but from a scalp sensitivity issue is a dead loss.
ETA: I went looking for alternatives. If you are looking for a cheaper version, the two salient characteristics are (a) natural bristles on (b) a cushion. So a natural bristle brush on a stiff backing (such as wood) wouldn't have both desirable traits. And I suspect -- but don't know for sure -- that a part natural, part nylon bristle thatch would behave enough differently to matter. Good luck! Mason Pearson makes mixed bristle brushes, but I have one that is "pure".