For my partner HP was the first book that broke through her dyslexia. She has zero approval for JKR's transphobia, but that will always be a cherished and important memory for her: the moment she realised she was reading freely without struggling.
I know multiple people for whom that was the case. I could be wrong, but I suspect that the font (Adobe Garamond, if forums are correct) had a lot to do with that.