The line takes a bit of getting used to. The trick is not to use it to underline the text you're currently reading but to keep the line a good distance ahead of where you are in the text.
Thanks, this is a common suggestion and I've tried a version with a shadow below the line. It is far more distracting especially when you use the autoscroll feature (play button at the bottom right corner.)
I find the already read text distracting. I would like everything within peek-ahead distance to be new text. Perhaps a white gradient below the line would work, or a three line tall moving white bar instead of the line.
I'm not sure if white or black gradient would be better though.