Idea for startup founders to measure Product-Market fit

Ever since Rahul Vohra wrote about how Superhuman measures product-market fit, I've thought about building software to make that process (4 question survey, data segmentation, OKR dashboard) super easy for founders. I know that nearly every startup struggles to measure product-market fit and at previous startups we would have been more successful if we were tracking using these metrics.

I recently discovered that last year Sean Ellis, who came up with the original product-market fit metric, collaborated to build a survey tool that measures it. His tool is free, and works well, but has a somewhat limited feature set.

Now I'm having a hard time deciding: Should I give up on the idea since a free tool already exists (and designed by the person who invented the metric)? Or is the problem real enough that I could build a more advanced tool that people would pay for? I appreciate any thoughts or ideas.

I honestly want to start something really badly, and coming up with the right idea has been very hard.