A small scientific study was done that concluded: "These results indicate there may be no benefit for translating print materials to this font."
People have been shopping around these fonts for years, first paid, and now free but in both cases the claims that they help aren't supported. I'd be particularly interested to see their effectiveness Vs. a placebo.
Except there's a study looking at it, with 12 participants, that found it didn't help. That's the best data we have, and current data suggests it doesn't help.
If you can find a study about Dyslexic fonts which supports their usage that would be compelling. Until then, that's what we have.
Also, the study found that it didn't help the participants.
Apparently there have been a few studies, and a thesis, investigating "dyslexic fonts", which found no real benefit. I can't find any evidence that OpenDyslexic and the like are helpful, meanwhile.