There are 3 versions of the GMT movement:
Asian 21j modded - the cheap one with varying opinions on reliability...doesn't operate the same as a Rolex gmt movement
Asian ETA Clone modded with Incorrect (Wrong) Hand Stack - ICHS - hand stack order is different from gen Rolex
Swiss ETA ICHS - considered reliable, but as with all ICHS movements, they don't function quite the same as the gen Rolex movement
SWISS ETA CHS - Works the same as the gen Rolex movement, but is often considered unreliable, expensive and hard to source
Most dealers will have the cheap Asian 21J modded, ETA ICHS, and Asian ETA ICHS. The bezel engraving on the GMT IIC can be good if you get the right one. Look for By-Tor's review and additional posts on the GMT IIc...he is one of the big authorities on it, and has posted TONNES of info comparing various versions of it. I think he got his from Precious Tim.