I bought mine from Napa and it is noticeably lower quality when compared to oem, I have it sitting on my desk I can snap some pics if you want. The section of the tube where the extension pipe slides in appears to be oblong, I highly doubt it would seal properly with the stock O rings. I will have the tubes soldered on to be 100% sure I have no leaks there. The fin count and row counts are lower that oem, and overall size is slightly smaller than oem. If you live in a place where heat is a necessity I recommend an OEM core. If you live somewhere like where I do where the lowest temp of the year is in the 30s at night time it shouldn't be a big deal.
Oh ya, and the aftermarket is copper whereas the OEM is brass.