I also like what others have written using this tool and posted here. It is interesting how we tend to write in simple language when we have constraints. That's the it should be. Not the constraints, but the language. Use jargon or too complex words and most of the times you have lost me as a reader. So, in a way, this app really helps you in writing the way you usually think or speak.
I think we can use this app to write proper stuff too. If we set it to 1 min, we can write much better stuff using this tool. Also, it would be great to have the functionality of not having the choice to delete what we have typed. Probably remove the backspace, delete and arrow-keys. I figure that I spend most of the time hitting backspace and deleting sentences. If I don't like the way I start a sentence, I should only be allowed to hit full-stop and start the new line and edit those things later.
I hit backspace many times when writing this post. It considers backspace also writing something. Another option would be to just not count backspace/delete/arrow keys as typing something.
This was really fun writing the whole thing set to 5 sec timer. I didn't know I could write so much without a 5 second gap.