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Best option might be refurnished one from Apple at $829. It has same warranty and Apple Care coverage as a new one. If it screws up, file trouble reports with Apple. If they can't fix it, ask for a replacement when the new ones come out (likely in the spring or summer of 2013).
 
Is this another instance of "some are good apples, some are bad apples" (pardon the pun) à la the rMBP? One just has to take one's chances? The firmware complaints are pervasive, but some people report no trouble whatsoever.
 
I got the 27" TBD from Best Buy for $850 as an open box. I just connected a LaCie 4TB Thunderbolt hard drive from the TBD. Plugged cable in turned LaCie power on and everything works without any issues with the MBPr. I also have a USB keyboard and USB hard dive connected to the TBD.

I did note one thing that may help. The magnetic power pigtail from the TBD Thunderbolt cable needs an adapter for the MBPr which easily disconnects for the MBPr. If the MBPr is closed the TBD will not turn on if this disconnects. So watch for the green LED on the power connector.
 
Is this another instance of "some are good apples, some are bad apples" (pardon the pun) à la the rMBP? One just has to take one's chances? The firmware complaints are pervasive, but some people report no trouble whatsoever.

That may be the case - my first TBD was faulty - the replacement has been perfect.
 
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