Textbook has two different versions, which to use?
Often if not almost always, "International Editions" (the monicker I know them under) are copies of expensive text books printed in emerging market countries (often India), whose legality I question...at least they are not licensed by the publisher for all I know. Someone here might have more substantial comments on the legal aspect - in fact, StrongBad does in his answer to an earlier question.

From the one I bought before understanding this, I would, in the future, stay away from them for their quality alone. I kept noticing that there were seeming errors where the text diverged in most cases from a supporting graphic; and there were graphics on almost every page. I carefully made a list of errata for the first 100 pages, and submitted them to the author. He was kind enough to reply fast, expressing that he was puzzled: none seemed to be true. I eventually figured out that the graphics and text of my book were from different editions of the original book...my version is essentially useless.