[andrewjl]

In your experience, how does that compare to measuring continual "use" of your product, like churn, cohort tracking, and others?

From the linked article, I'd say the "what's missing" question is perhaps the best signal, if customers list tons of missing things yet continue using the product despite those shortcomings, as measured by usage stats for instance, then you know you not only have PMF but also the beginnings of a lock on the market.

[kpowerinfinity]

OP here. Always a good place to be in. Hard numbers is more valuable but you need to think about how to address the concerns else you will hit a glass ceiling, or the moment they find an alternative they will jump. Thinking about lock-in is very important.