Should I start charging users? Or learn more?

I've been building https://truestory.ink/ in public using my twitter page and at the end of this month I will be enforcing my pricing tiers.

At the free tier, users can record and replay 100 sessions a month. They would have to upgrade to replay the sessions that are recorded after the 100th.

I only have two users. One of them will have to upgrade based on his usage. I'm worried that if I start enforcing pricing tiers I will loose the customer that I'm learning a great deal from.

Any advice?