Product review (4 stars): Good, but could be better.
I read some of the negative reviews and gave this a try anyway. Fearing that I may end up getting a used repackaged product (as mentioned in some of the negative reviews) I made sure to pick up a TDS* water meter/tester as well. Not only to make sure I got a new filter from this seller, but also so I can test the various liquids used around my home.

As I'd mentioned in my review for the TDS* water meter/tester, my tap water is hard so I used the baseline measurement (PPM's) of a bottle of Poland Spring water. My main concern about this filter or my refrigerator water line in general, was that it wasn't going to make too much of a difference drinking water from the tap versus one that came out of this filter. After my baseline measurements, my concerns were put at ease.

Below are results from my tests:

(measurements in PPM)
0-50 = Ideal drinking water
50-100 = Carbon filtered water
100-200 = Hard water
200-300 = Marginally acceptable
200-400 = Average tap water
400+ Very high TDS contaminant level

--My household baseline--
Bottle of Poland Spring = 18
Tap Water = 281
Gatorade = 260
5 month old filter from my refrigerator water line = 240
New filter from my refrigerator water line = 200
Melted ice (4 hours) = 293

So what did I learn from this... My tap water isn't too bad, this particular filter can probably go another month or two, and I really need to clean my ice maker. The good news is that this filter removed 80+PPM's of TDS* from my tap.

*TDS* - Total Dissolved Solids are the total amount of mobile charged ions, including minerals, salts, or metals dissolved in a given volume of water.