The most indicative (and universal) measure of building something people want is retention.
The trial period is where the rubber hits the road. You’ve made promises up to this point and even got some people to buy into them. Congratulations! Now it’s time to start delivering on them. That’s easier said then done. Not because your minimum viable product is less than perfect, but even getting customers to experience your MVP at all can present challenges that have nothing to do with the core product itself.
Another brilliant post by Ash Maurya that explains his reasoning behind trial periods and how Cloudfire handles theirs.