Perhaps the best FREE thing I've found for several years

Databases work great when fresh and clean but over the years you seem to encounter more and more performance issues. Over-enthusiastic developers brimming with confidence can quickly overload tables with indexes or make changes without thinking about scenarios outside their ticket. Business growth can lead to server strain if you aren't monitoring your infra vigilantly. Queries that once worked well can suffer over time and you need a good tool to dig in to the data. PMM is excellent for these kinds of use-cases.

I initially found the vast quantity of data presented to be overwhelming, but that is where I needed to raise my knowledge to understand the DB internals better. If you feel you don't know enough about your database performance the dashboards will keep you busy for a while. The Query Analytics tool may also be insightful. My only gripe is I wish there was more documentation on explaining some of the data for less experienced MySQL users.

The data presented is pretty easy to view and examine. I have had no issues exploring data over time, filtering down to specifics, or managing users. The one area I feel could be improved is dashboard names/menu navigation. The menu feels like a limitation of the Grafana framework, and the dashboard names seem just a bit similar so you may head in the wrong direction initially.