This is not needed. If the agent has no problems you don’t need to update over the next 1-2 years.
Advantage of an agent is the possibility to extend the functionality. It gives more information about the real Synology system. Like running processes with CPU and memory consumption.
The SNMP service on the synology devices are not the best, i have some of these systems in monitoring environments and it happens from time to time that the SNMP service hangs.
But in the end i would combine the agent and SNMP in bigger Synology devices. In smaller ones SNMP is enough.
Disk status, Raid status, Fan and PSU i would do with SNMP and the complete operating system with agent.