When we started Pubb.at, we aimed at paid communities. I wanted to make a good platform for community builders to host their members. With some hustling, it did gave us some MRR. Not a lot but was able to make couple bucks.
It gave us a sense of feeling that things are moving forward. You didn't need a million users to feel that, since the money talks itself.
But lately I have been working on a new app. It's called Gumdrop.ai, a dating app that matches by humor. I am still in the validation phase. I did tons of customer interviews, I got some really cool data. I was able to get a lot of people sign up for the waitlist.
But it felt weird because it will be a free app. Money doesn't translate my growth anymore. It gets very tricky. MRR/Rev is very direct, but user number is not. Depends on different industries and apps, user numbers can be very different. And if it's a free app, most likely you will face a lot of competition, because if there was no solution ever before, you will charge them.
Paid and unpaid is two different games. IMO paid is an easier one to validate, if you don't make money then it doesn't work. But unpaid is tricky, harder to validate.