I haven't got that much personal experience with the Platypus though I use their 4.0 gravityworks. I have yet to have any issues with it nor have those I have come across. Heck, this past weekend there were 3 other groups running the same set-up. I'm the only one that was using the carbon-filter (turns out there is no taste in the water here to filter so I'm leaving it at home next time).

I have, however, heard a few issues both on the forums and in the field of the sawyer system blocking easily and not wanting to back-flush or clear. The platypus as long as you follow the directions works great.

(start the flow, let about 1/4 liter or so come in, reverse it to purge the system of air, then it flows quickly. When you are done filtering back-flow about 1/4 liter to clear it out. That's it.)