I think $6/mo. for fast, privacy-focused analytics for small sites is very reasonable.
There's no ad revenue to support this business — the website owner is the customer, not the product. That is a different business model from Google analytics or WordPress free analytics.
Depends what you use it for; if you're just vaguely curious about how many people visit which page on your site – which is probably what a large part of people use it for on their person sites – then $6/month is comparatively a lot, especially if you consider there are competitors which offer it for free (not just GA).
There's no ad revenue to support this business — the website owner is the customer, not the product. That is a different business model from Google analytics or WordPress free analytics.