I've never used the BeFree, but I use the Sawyer Mini constantly. I primarily use it with an MSR Autoflow for camp applications, but do keep the included straw stashed in my pack for quick sips here and there, and I'll occasionally pull it off the MSR and use it with a bag, making it more versatile.I like the fact that it can be used in-line as a gravity filter, it's very reliable, easy to backflush in the field, small and light enough to carry a second, and it's just a little over half the cost of the BeFree and most other cartridges.
Yes, I have used a Sawyer Mini for a while, but the BeFree makes filtering so much easier, it was worth the extra dollars. Either filter should last for years anyway.
Just returned from a backpack/car camp/flyfishing trip from the Cottonwood Lakes to the Sawtooth mountains. On our backpacking portion of the trip, my buddy brought his brand new MSR pump filter, another friend brought his hang bag filter (forget the brand) and I brought my Katadyn BeFree.
Both of my friends filters clogged (hang bag) or broke(MSR) and clogged during our 5 day trip. The only filter that kept working perfectly was mine. I think that's a pretty good testament. It also worked great while flyfishing the Copper Basin in Idaho on my car camp session.