I bought the 3 pack when I bought the container. It was the best deal. I do find that sometimes the filter slows down, but if you soak it for 15 minutes like they recommend, it starts working normally again. Also, I have well water with lots of minerals so I think it happens more often than it would for municipal water.
Yes the water product after filtering is clean, in appearance and taste. Of course I don't have a way to running a bacteriology test to confirm how clean. Still I can attest my body feels better drinking this water vs. from other filters or worst unfiltered.