It really depends exactly on what you're trying to monitor about the devices.
You can start with Health Check Point (HCP), which can even show you the data in SmartConsole through an extension: https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut...
Skyline (currently in EA) can also be used to export performance data to anything that supports OpenTelemetry (we support Grafana/Prometheus).
See: https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut...
cpview (executed from the relevant gateway) can be used to view some real-time performance data and is useful for troubleshooting performance-related issues.
You can also monitor with SNMP tools, though you have to know exactly what MIBs to probe.
Indeni (a third party tool) is another possible option.