Interesting you should bring this up as we are currently in the process of moving from Datadog to Prometheus/Grafana. What we've found is all the time you save

Interesting you should bring this up as we are currently in the process of moving from Datadog to Prometheus/Grafana. What we've found is all the time you save in not setting up Prometheus we lose in support tickets to Datadog to get them to explain undocumented functionality and hidden "magic" they put in place. With Prometheus/Grafana the answers are always out there because of the sheer number of people out there. We've even resorted to sending known metrics on known intervals just to understand what Datadog does differently for monitors vs graphs. Also the majority of the time for a monitoring system is not spent on setting it up but rather on generating the dashboards and alerts. Also with all buys systems there is a hidden costs in managing the legion of user accounts to access these new services. It's rarely as easy as just setting up SAML or single sign on. The final thing that people never talk about is cost. Yes there is the cost of an engineer to set it up but often that costs is cheaper than the bought service. This is especially true of pay per api call type services.