Datadog is a pretty amazing product, and if you are careful and use it in the right way, it is very powerful, and cheaper than rolling your own LGTM Grafana stack (or similar). If you are not careful, or at a decent scale, you can easily spend obscene amounts of money. The metrics pricing is completely insane for example, and its easy for people to emit high cardinality metrics from apps and explode your bill. I think by this point you need to run an internal solution, and that is when it makes sense to double down on a combo of elastic, and grafanas stack for logging, tracing and metrics.