I just bought the Katadyn BeFree water filter this past week and have given it a couple little trials on some hiking trips. I am very impressed! It is extremely light and has a very fast flow rate. Click on this link youtube video if you want to see the filter in action.
Advantages of the 0.6 Liter BeFree filter:
2.1 oz dry (about 2.3 oz wet) The lightest filter I have ever found.
2 L per minute flow rate. The highest flow rate of any filter I have found.
4.5 cm mouth makes it easier to fill the bladder from a lake or slow flowing water
You can fill the filter with water and hike with it in your side pocket. (Unlike the sawyer mini)
Disadvantages of the 0.6 Liter BeFree filter:
More expensive: The 0.6L version was $40 at REI. They sawyer mini is only $24.
So far that is the only disadvantage I have found!
A great filter! I will add more information after my 5 day trip next week with my wife.