Question about Ubiquiti SFP+ Modul UACC-CM-RJ45-MG

Coming from what end on init7? Native they're fibre, not RJ-45 like this one. So for Fiber 7, no. If you're using Hybrid 7, with (e.g.) a Nokia bridge (they have that option), then yes, this works.

But I wonder if there's some misunderstanding. This plugs into a device, so what device would you plug it into?

No, you get a glass SFP+ module from init7, and you can then use this 10GB module with a UDM Pro as an uplink to a PC or 10GB switch or NAS, it is Multigiga, but there is also a direct 10GB SFP+ module or you use a DAC cable.