@oldbutndy I don't totally understand all the N10 versions (and I really tried at one point!) but Ruben, the porter/maintainer, has said that the T-Mobile / Metro versions should work, despite what the device page says. You'll find at least one other post in the N10 section of the forum that shows someone using an N10 Metro, in USA, who now has VoLTE.
I think no one wants to guaratee it, as it's not what the porter uses, but it sounds like it'll work.
I think Factory Unlocked generally just means it was never locked to a carrier, but doesn't mean bootloader is unlocked.
I found downgrading android, after unlocking the bootloader, to be a pain on the N10, but I'm pretty novice at that sorta stuff, and I got it done in the end.
Seek instructions, get the MSM tool, understand EDL mode. You'll figure it out!
Good luck!