I don’t think that $29 is too expensive for a webapp. I’m a bit worried about paying any amount for a product I don’t own and which could disappear overnight. When buying traditional software that we install, even if the company goes out of business, we still have the software we paid for. It’s obviously not the case for a webapp and given how new your product is, this might refrain potential customers.

As for free vs paying feature, I’d only give the time taken to complete the exercise and the wpm, and suggest upgrading to the paying version to have more stats.