Product review (4 stars): Expensive but works well
The filter is certainly not cheap and only lasts about 4-6 months.  However, it certainly makes a difference.  I can taste that the water is better when I change the filter.  More impressively, I use water from my fridge to fill humidifiers in my house.  I started getting the dreaded "white dust" showing up all over the place.  Days later the change filter light lit up.  I changed the filter and the white dust went away.  So, it's definitely working.