Product review (5 stars): Water Filter Works Fine
The water filters work great as far as I can tell.  The only way I've actually tested the water is by tasting it and it tastes just like it did before.  It was pretty easy to install (figuring out how to shut off the water supply was the most difficult part).

One note is that immediately after installing it you should run quite a bit of water through it before using it (as it says on the directions).  A couple of cups of black water came out while running water through it initially.  After that everything has been great.