I just picked up the Beefree filter and this thing is great!!
It has a wide mouth at the bladder fill (43mm) and the nozzle at the end of the filter will fit into a Smartwater bottle.
Water comes out fast and will fill a 1 liter bottle in no time and is easy to clean.
The bladder is 0.6 liter which means you have to filter twice for a 1 liter bottle but not a big deal and it weighs in at about 2oz.
I have quite the collection of water treatment gear but I think this may be the one!