Tracking people almost always a bad idea in my opinion.
Even if they get something in return like early access to something.
Even if they're happy to accept being tracked.
There just isn't a good justification for it in most cases. For a start, most sites that track users don't even use the data they gather. They're just gathering it because they're think they're expected to. So many sites implement Google Analytics, Hotjar, etc and then use the data as nothing more than a web counter. That's beyond infuriating to anyone who thinks privacy is worth fighting for. If you're going to violate my privacy, at least do it for a good reason.
In the case of the article there could be solid reasons for hoovering up lots of information about users. But really, unless you're in a massive company with significant resources, all of that perf data is just going to sit in a database and a senior might occasionally look at the dashboard overview and think "We should make our images smaller." or "Huh, users have a sucky time when they're on Android. Oh well.". Those are not good reasons to gather real-world user data instead of relying on Lighthouse scores. Lighthouse is "good enough" for most people.
I imagine that a frustrating part of working on web perf is that small companies and startups don't have the resources to do it well, so they end up cargo-culting what Google does but without spending time or effort to make good on what they might learn.
To be fair to the author, I'm much more at fault here than they are. I have no doubt that the article is aimed it at a much smaller audience (the web perf community), and now I'm here saying it's not applicable in a much broader context because it was posted to HN. I apologize to them for that. This is something I care about and it was an opportunity to rant. :)