The Tidepool automatically categorises my research tabs. Is the concept of pricing reasonable?

Tidepool is a browser extension that tracks how I do research and categorizes all relevant tabs into sessions. If I spend an afternoon researching electric bike battery technology, then Tidepool groups all these tabs into one session, creates a brief description of what it is, and allows me to close them all without getting lost.

This project was created to solve my problem of having 60 tabs open. I've used it for two months on my own before showing it to anyone. Currently, around fifty people use it daily, and the feedback I have received so far has been very constructive and friendly.

Three active sessions are included in the free plan. The paid plan, which costs me $6 per month, provides unlimited sessions and search through previous ones.

What concerns me is that people do not like to pay for browser extensions. I have encountered two extremes here: either an extension is overpriced or offers all features for free until the developer crashes.

What seems to be reasonable for sellers/buyers of browser extensions? Would you prefer to pay once, pay monthly, or set your own price? And if you have already released something similar, what should you know about trust and permissions beforehand?