check the recycle number - as I understand it, if its 2 (PETE, HDPE), you'll be fine.
of course, there's also happy stories of people using other products and having them work out just fine as well.
i can see where you might not wanna take a chance, on the other hand. if its a short term (weeks, not months) secondary, the chances of oxidation are gonna be limited, and its cheaper than buying another glass or better bottle carboy.