The T-Mobile store bricked a few devices using the sd card, but I can't imagine that it was the update files fault. Either the employee didnt know what they were doing, or the sd card had some bad files.
Regardless, many phones were fine after using the file, and if you want the official gingerbread update, I highly reccommend it. But whatever you do is up to you.
It is the T-Mobile update, so yes, you would be locked into T-Mobile.
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