Product review (4 stars): Not Standard 53 approved, but Standard 42 approved.  Works well.
Easily replaced my old filter.  The water flow is tremendously improved - should have replaced that old filter years ago.  One of the reviewers discusses the differences between the original replacement and this one in respect to NSF/ANSI Standard 42 and Standard 53.  This is Standard 42 certified, but not 53.  While I'm not a chemical engineer and don't know the specifics of exactly whether it failed the Standard 53 testing or just didn't attempt it, I did read that this model allows fluoride to get through - one of the Standard 53 metals to be eliminated.  That is always a debate about Fluoride and whether it is advantageous or harmful when in drinking water.  However, with the current U.S. standards in water delivery, I don't think that removing all of the heavy metals is as big a deal as some make it - of course if my water was high in lead, I might change my mind.  I would normally drink water from the faucet here at my home and this filter at least clears out the chlorine from the taste.  To my knowledge activated carbon is activated carbon and it is pretty much a commodity - by the way this is activated coconut carbon.  The testing procedures in these cases may be the difference for some buyers.

I am not concerned, but if you are, then you might want the original equipment replacement.  I'm okay with this one.