There is a free plan actually. At the bottom of the page: https://histre.com/pricing/

I'll make that more prominent.

Exactly the same feeling. It is not clear that the service is paid because it is mentioned that the extension is open-source. I understand you need to keep the lights on, but it is better to let know about about the pricing I upfront.

You mentioned there is a free tier, but can't see what's supported on free vs the paid tiers. It'll be better if you add the free tier and features to the comparison chart. Just my two cents.

A great idea regardless, kudos.