A roll your own open source method works if you have a good low level understanding of what you are listening to and can organize your own alarm thresholds and groupings etc. Dealing with a large number of modbus/BACnet endpoints with vendor specific device profiles and PLC logic means the vendors backend systems will handle events and trend paterns better than what most facility teams can put together. However, the history retention data by itself will have more flexibility to do it yourself, I do agree with that.