Product review (5 stars): The NSF/ANSI 53 Certification is the way to go.
This is the Genuine article. There are a lot of long-winded reviews about these things So I'll keep it short.

This is NSF certified for both aesthetic effects (NSF/ANSI 42) and health effects (NSF/ANSI 53). The cheaper versions you see are only certified for one or the other, mostly aesthetic effects like taste or smell, but DO NOT get rid of the stuff that may make you ill.

We're on well water so it's a no-brainer but those of you on municipal water who trust the city/county/state to take care of things should consider spending the money and get something that has the NSF/ANSI 53 Certification. Those cheaper ones won't look so good when you find out your water smelled and tasted fine....but made you sick. (see Flint, MI)