Before you use the Platypus bags, check them at home. I didn't have any problems with a couple of Platys that I bought last year, but I did have a problem with a 2-liter that I bought this year: I couldn't get the threads to seal, and ended up with dirty water leaking down the side of the filter and contaminating my drinking bottle and clean water. Mine may have been a fluke (or operator error), but you don't want to take the bag into the field untested.

My own solution was to simply switch to the 2-liter Platy Gravityworks, and eliminate the issue entirely. Probably an over-reaction on my part, though. The Sawyer is an awfully good filter, and based on about a year of weekend use, I'd recommend it highly.