I have used both the Sawyer Mini and the Sawyer Squeeze. The Mini is fine for a while when filtering perfectly clean water, but it will clog up very soon. I have used it on the Arizona Trail and at the end it had become very slow. The Squeeze has about twice the filtering surface (at the cost of being somewhat heavier) and suffers much less from the clogging up problem and filters a lot faster. Therefore, you'll find many Minis in hikerboxes along long distance trails like the PCT, because everybody abandons their Mini and replaces it with the Squeeze. This includes the ultralight crowd that weighs every gram.
My Sawyer Squeeze was used on the entire length of the PCT and last year also on the Bibbulmun Track in Australia and it still works great (with regular backflushes). I estimate it has already filtered 750-1000 litres of dirty/ suspicious water in its lifetime.
As mentioned by some, the squeeze bags that come with it are useless for their intended purpose. Most people screw the Sawyer on a Smartwater bottle (the thread fits, it's a standard thread) and squeeze this bottle. It's much easier to fill. The squeeze bags can still serve a useful purpose though: I have cut off the top so I can use it as a lightweight (and flat) tool to scoop up water from puddles or very shallow streams, because without that filling up your (dirty) bottle or bladder can be a real pain in areas where water is scarce.
Because I'm lazy, I don't squeeze anything but use my Sawyer in a gravity setup. I use a 2L Evernew water bladder as my dirty bladder and screw the Sawyer on top (note: use Evernew, a Platypus won't work properly because it uses a proprietary thread that is slightly different than the standard used on most softdrink bottles, the Sawyers and Evernew). I have connected a wire loop to it, so I can hang it from a tree/ fence/ rock. Then I have a hose (from a platypus drinking system) that I connect to my clean bladder on the ground. The 1 metre water column in the hose creates enough pressure to suck the water through the filter while I'm relaxing with a snack. I think it works great. The only downside is that I have to carry the hose (57 gram), which I don't use for anything else (I don't like drinking systems).
In places like Scotland, with plenty of clean but sometimes suspicious water, I can't be bothered with filtering and just pop in a chlorine tablet when in doubt.