The good point is that it reads smoothly. It highlights the paragraphs, which is helpful, but not the words being read. Therefore it is difficult for me to know where in the paragraph we are, if I want to start follow the reading at any point of the flow.

It opens a little window on the top right of the browser and this window closes down if you click somewhere else. This is not useful if you like to take notes while being shown where in the text the reading is happening.

No images are shown in that window, only text. Therefore sometimes I don't know to which picture I should look at in the original page (in the text sometimes it says "...as demonstrated in the picture on the left"). I tried to scroll down on the original text whenever I heard that but then the little window would close and I'd lost myself once again. Too much cognitive load.

In my opinion it would be best if the read aloud took place in the original page, not in a popup window.