Typing Analysis to focus on our weak keys or words
On improving typing skills, Wikipedia says:
"While practicing, it is important to ensure that there are no weak keys. Typing speed is typically determined by how slow these weak keys are typed rather than how fast the remaining keys are typed."
There is a topic suggesting a list of worst words (denied, planned for supporters): https://10fastfingers.useresponse.com/topic/practice-your-worst-words
I suggest adding a feature to map our weak keys, just like this:
His tool is great, but he misses all the great structure of 10FastFingers (other languages, storing user info, using common words, etc.).
Whether this is to be available just for paid users is up to your strategy.