Just reading the example paragraph, I did feel at times speed was increased, but there were times the highlighted letters caused my brain to assume the wrong word, and when that happened it took extra effort (& time) to focus on the actual word.
Yes I understand that. Optimal is then if you have set your individual reading setting with Bionic Reading.
And what you have to remember is that your brain has already absorbed the words. So your eye jumps back instead of gliding over the text.
However, this will turn off and you will find that you understand the text without having read every letter.