I like that there is a fallback to read the full text, but why are there two such app modes? I think if the main (non-popup) one should absorb the other's features like scrolling and bookmarks.
For some texts the layout is also important to understand the context. Poems, structured text, paragraph breaks. If you read word by word and stumble into block of structured text, it's a lot of friction to figure out. I would love a background low fidelity representation of paragraphs, like the minimap in code editors, with the current word highlighted there. It could be passively monitored for places to switch mode to reading the full text, and to keep spatial orientation around character dialogs and such. It would have to not draw attention to itself though.
The theme circle icons are not useful, they should preview text background and color.
I see Dyslexic font is already built-in!
Code is not available? It would be fun to hook this to browser extension to fast-read article in a ReadKinetic popup.
I didn't mind the controls at all, they are obviously for touch and not mouse and it seems inspired by video player controls. This is a kind of app that you spend hours with, so better to have more features and options than to be beginner friendly. Very nice app, I like it so far.