Well, without looking into it further, I am thinking that the difference would lie in the electrical interface somehow. A quote from the second site:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>If your car seats are electric you already have a power source under your seat for these seat heaters and it comes with a 24" (600mm) Power Lead to splice into the Seat Harness<HR></BLOCKQUOTE>
Both sites posted temperatures and are the same ... in these cases I just go with my gut feel ... especially on the net. If you have a good feeling about the "GM Authorized" ones, get those. If you get the others and something goes wrong you will always wonder.
I couldn't find anything from a technical standpoint to choose one over the other.
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