Unhappy [Q] Updating an unlocked T-mobile Note 3 with latest firmware.. Is it possible?? HELP

Hey guys,

Saw a very good deal on ebay india, the seller is selling an unlocked version Note - 3 T-mobile (US), so it can work on Indian GSM carriers.
Now, if you see the description: it mentions:
"The OS Software is Unlocked to Work with all GSM SIMS.
You are not supposed to Update the OS Software as Unlock code is applied to it"


2 quick questions:
1) Can you help me understand what does the seller mean here? The device will obviously be running on JB, so i wont be able to update it to the officially released Kitkat? Will manually flashing a firmware from say Sammobile, revert the unlock code and make the device useless?
2) Buying a US phone for Indian use.. Will i miss out on any features? or will it be a problem in any way??
Please help me out guys