The only high quality GMT IIc currently available is from the N-Factory, which would explain why they all look the same to you; yes?
The tells would be that the replica has no AR coating under it's magnifying cyclops lens. Also, the numbers on the genuine ceramic bezel insert are pure platinum and on the replica are pure paint.
There is an interesting school of thought on the movements available in this watch, which is exactly opposite other watches and that is this ... the asian 21j movement is the wise choice, since it is a purpose-built GMT movement. If you buy the GMT IIc with a Swiss ETA movement inside, it is a non-GMT movement with some extra gears and clutches screwed to it. Not optimal.
note: there is talk of a new breed of GMT module for the reps .. it's only been reported on ONCE and it is a huge improvement over the existing GMT modules, making it safe and wise to purchase the Swiss ETA GMT IIc **if** this new module is inside of it.
Who can guarantee it's in there? No one.