Product review (4 stars): Lasts about 6 months before water tastes "funny"
It's a filter, what more can be said?
In my fridge, with a family of 4, 6 months is about right before I start getting a plasticky taste in my water, especially in the morning when the water has been sitting overnight.  Replacing the filter immediately resolves the issue.

So it your water starts tasting a little plasticky after a few months, don't put up with it, simply replace the filter.  I took one star off because the price really shouldn't be over $20, but otherwise works just fine.