- I'd prefer if the words not typed were in a lighter shade of grey so there were greater contrast between them and the words I've completed. I know this would reduce contrast with the page but I found the fact that they are such a strong grey to be somewhat of a distraction. Different people will have different preferences here, so maybe a slider or knob that can be used to adjust the contrast of yet to be typed text would be helpful.
- The fact that you can't correct mistakes is a huge annoyance and breaks my typing flow. It also tends to lead to runs of errors since I'll make a mistake, hit backspace, and then carry on typing, meaning I get an off by one error in the next few letters. I understand that you want to help people type with fewer errors but the reality is the way it works at the moment interrupts my flow much more severely than correcting the error would (and leads to far more mistakes), and you can still track the number of mistakes I make even if I'm allowed to correct them. I'd say the ability to correct mistakes should at least be an option that can be enabled or disabled according to the preference of the user.
Hope that's useful and, once again, this is very cool.