The recordMetric call creates a single Custom Metric with a name and a value. That's all. It's a single method call.
Ultimately I'd like to drive some dashboards and ideally alerts from the data points sent.
Can you elaborate on the kinds of dashboards you're looking to set up? This should help us in suggesting best practices.
Circuit Breaker disables instrumentation. It would affect @Trace annotation, XML instrumentation and the like. I don't think that it affects recordMetric.