Yeah the toggle is there-double press and it locks it into playing continually. But if you didn't find it, that’s on me because it’s not discoverable. There is that line of text at the top which says hold to read, left/right to scrub, and obviously if that isn’t making clear there is another mode of play lurking just behind a gesture no one ever brings up.

I did default to hold because the read stops the instant you are not reading – if your attention is drifting, words aren't racing on ahead.

Which felt right for an application whose whole purpose is concentration. But you are almost certainly going to react the way most people will, and there should be an easy toggle instead of one you’re only likely to find when you stumble over it by accident. Scrub is already mapped to left and right-up and down would be an excellent match to speed, never thought of it that way until you said it. Let me know how you get on with the longer pieces, that’s where I’d expect either that it just clicks (or fails miserably).