I think there is no single font that will help "dyslexics" because many students in our practice have told us different preferences in the font sizes, shapes / serifs, colors, and character spacing re: readability.

As a group, there are some scientific studies which show the need for larger font and increased character spacing, among other issues. The option to customize will help some people though.

In our dyslexia practice, many kids tell us that they prefer Comic Sans with a larger font...the extra shaping of letters helps distinguish mirror letters like b and d.