The ELK stack is really fancy next generation "tail -f | grep" in a web browser. Which is awesome and really important, but a very different problem from "tell me how many users have used my app for three or more days in a sliding thirty day window".

I've been eyeing a switch to the ELK stack from Mixpanel + Big Query for an app. Could you expand on what ELK is useful for?

At work we use it for log aggregation (specifically application-health telemetry from a mobile application). Very useful in debugging.

Oh god, don't do it. Running E is a bitch, and incredibly expensive. To get L running over any kind of load, you need to do so many hacks.