Okay, so I played with this for a few more minutes and this is my feedback: I think this would be great for children with reading issues. It would be great as

Okay, so I played with this for a few more minutes and this is my feedback: I think this would be great for children with reading issues. It would be great as a 'feature' that can be turned on or off on an operating system (on the desktop, tablet, or smartphone). It feels almost like 'training wheels', and as such, I think it'd be great. However, I do now realise that the line underlining the text can be distracting for someone who no longer has trouble following from one line to the next. Also, it is too easy for children to use this as a crutch, and may actually hinder muscle improvement if used for too long. Also, like I said, I don't really have reading issues anymore, but I can see how this could've helped me when I was a kid. I definitely would be interested in reading the results of this tested on kids. As another person said below, my primary schoolteacher also suggested we use a paper to block out the bottom text when reading line by line, and this did help, but I think I was very self-conscious to actually do it all the time. You're on to something! Edit: Added clarification.