Bionic-Reading is a technique still under study (see Statements at the top of BR Document or the photo below). So it seems to some people that it doesn't work (or rather it's less readability), but I think it's going to improve over time.
And... I'm not the designer of Bionic-Reading, nor am I the researcher involved. So there's nothing I can say about this.
I'm sorry if I didn't help you. Thank you for reading it.