I’ve been running OPNsense as a VM in Proxmox for a year on an AliExpress box that doesn’t have ECC. If I might ask, why do you have a requirement for ECC?
Before this box, I ran a Dell R230 with pfSense but got tired of the noise and 40 watt power draw.
I’ve had zero issues without ECC, so I’m just curious about your need for it.
NPM is awesome until you have a weird error that the web GUI does not give a hint about the problem. Used it for years at this point and wouldn’t consider anything else at this point. It just works and is super simple.