The sg1100 and the Brume have the same chipset. I wondered the same thing 6 months ago. There is a Opnsense.img for the espressobin v7, which the Brume and sg1100 used as a mock during production. I just don’t know how to compile it or use it.
Pfsense has not yet released their arm version, so it’s impossible ATM.
Here is my thread: Brume MV1000 - possible to load Opnsense?