The size of the agent will be minimal and will vary based on the agent type. For example, a Java agent will be around 10MB in size. You can also check the agent's load on the application using this link.
https://www.manageengine.com/products/applications_manager/help/apm-insight-java-agent-performance-report.html
You can modify the Apdex calculation by modifying the 'Apdex Threshold' in APM Insight agent configuration. Kindly refer to this help to know more. Based on your Application response time requirement, consult with your application team and make an informed decision.
It allows us to track crucial metrics such as response times, resource utilization, error rates, and transaction performance. The real-time monitoring alerts promptly notify us of any issues or anomalies, enabling us to take immediate action.
Reviewer Role: Research and Development