As a small company using one of the providers (https://usefathom.com/) it offers us choice. We don't want to build and run our own analytics and we don't need the vast features of a Google Analytics or similar either. Even without the privacy benefit the set metrics we get now acceptable. We don't have, e.g. a growth manager who needs to report these, investors who question the or make decisions when one metric looks off. Legitimacy didn't come up once during our migration and we didn't look too closely to compare to our previous provider (Google Analytics). It's not the core of your questions but there's usecases where less metrics, less accuracy is good enough.

Personally I have a background in metrics and reporting tools. I've been tasked to find and explain 0.3% differences between two reports or have cookie related (or timezone related) code getting reviewed by other engineers at previous companies. With millions of dollar at stake, Powerpoint meetings or investor or financial documention it makes sense to question every definition and the whole data pipeline.

> Coolness over effectiveness? What's all the fuss really about?

Ok, I admit, there's a bit of coolness factor. Paying $25/month to a small bootstrapped company (with a great podcast) beats feeding data to an ever growing global player (Google).