We absolutely support you: https://mixpanel.com/free/ - instead of a $30-80/mo plan, it's free! Of course, if you're averse to placing a badge on your site, then that's a different problem.
Could someone explain why this does not qualify as an ad?
The shadow rule is that any linkbuilding method is kosher iff no one has figured out a way to scalably achieve rankings on very competitive terms with it. For example, citations on the footers of blog templates were 150% A-OK right until people found out that was a scalable way to rank e.g. for e.g. [printer cartridges], [payday loans], etc etc. See also widgetbait, quizzes, etc etc.