The Korean (950N) variant doesn't have the 1700 for T-Mobile. That variant would work better (as in more thoroughly) on att since they use 1900, which the phone has. The phone will still work and as long as you're connected to the other bands, it'll still be usable. The other thing is that the N variant won't have much dev support, if at all.
Correct. The Korean variant doesn't seem to be affected from the OEM unlock nightmare.
However, on the bright side you'll have a monstrous 256Gb of internal storage if you went with the Emperor Edition. Marry that with a 256Gb Samsung Evo Plus and enjoy your 512GB Beast.
::iunlock::