Product review (5 stars): Meets NSF/ANSI Standards 401, 53, and 42!
WATER QUALITY AND SAFETY
I have a 2005 Whirlpool refrigerator and was looking for a filter that met NSF and ANSI standards for removing contaminants and not just improving taste.  I had a hard time figuring out whether this filter met the standards, as the information I could find only said it was NSF certified and did not list the specific standards or claims under each standard.  This meets NSF/ANSI 42 for taste ("aesthetic effects"), 53 for "health effects," and 401 for "emerging contaminants."  I'm attaching a picture of the NSF certification on the package that I received, but you can (and should) verify the certification and standards claimed by Whirlpool by searching for the filter under Whirlpool's old model number NL240V on the NSF website.  I was concerned about Atrazine (a pesticide that I found in my water) and lead.

FILTER COMPATIBILITY
Several reviews mention that this filter does not replace part #4396508.  My Whirlpool manual listed my replacement part as #4396508, and this fits.  I entered my model number on the Whirlpool website to verify compatibility.  The top of my filter looked exactly like the old one (which was a #4396508 left by the previous owner).  I don't know whether there are counterfeits or bad batches floating around, but I bought mine directly from Amazon and not from a third party seller.

OTHER NOTES
*Replacing the filter has really improved my water flow.
*You have to flush four gallons--a lot--through the filter before you use it the first time.
*Replace every 6 months.