I read about this quite some time ago. Seems like they found out, that this doesn't really make a difference in reading speed or comprehension. "Byonic reading" is basically just homeopathy for formating texts.
Posts like the one in the picture works for various other reasons - just not because of formatting. They are advertisements, as "bionic reading" is a proprietary solution.
I have ADHD, originally diagnosed as ADD, and I had a kind of choppy reading experience with the text in OP's screenshot. Speed was about the same as with "regular" texts, but the bold syllables were a different/new type of distraction. I could imagine, however, that with the right font, the method might be practical for me.
Stuff like this feels weird at first but your brain gets used to it fast. I've switched to using the OpenDyslexic font on my Kindle and when you first see it, it's very weird. But after using it for many months I don't even notice that the letters are shaped differently anymore. Your brain will normalize the letters into looking like standard letters. I can only notice that the shape is different if I quickly switch between fonts. Using this has drastically improved my reading and attention span with much less fatigue.
I'm not sure if this bold method will have the same effect but if it does I think it would take some time to first adjust, and then stop seeing the bold letters as bold. In my experience with the OpenDyslexic font when you're focused on the difference, it's not helping, it's only when you stop seeing it and are focused on the content that you realize you're getting the content faster and with less work. Focusing on the letters themselves is doing extra work. If this method has utility it is in instant recognition without extra work. It's not really possible to understand if it helps from reading a blurb because you're going to be focused on the bold and not the content. I'd love to read a full book like this just to see how it feels.