I don't think that there's a single ONU SFP module on the
official list of compatible hardware. There are a few threads on this forum about using various GPON SFP modules with MT and mostly the gist of them is that things either don't work at all (with some rare exceptions) or are extremely tricky to configure.
The problem is that GPON SFP modules are essentially ONTs, compressed into a SFP module footprint. That includes also software, running on ONTs, config and management interface. Not to mention that in many GPON networks, network operator provides ONTs with specific settings applied ... and most of them don't want to hear about using 3rd party ONT devices. So getting ONU SFPs to work with any particular GPON network is very tricky (in your case this part seems to be simpler than for most GPON users).