IMHO Sawyer needs to craft a screw-on funnel to facilitate filling the bag through that tiny opening. The only time I find filling it simple is in a stream deep enough to immerse the bag, facing the flow. Lakes are less easy (especially if you're avoiding murky water next to the shore) and seeps and trickles are about impossible.

Since realizing it can be rigged as a gravity filter I'm liking the concept better.

Cheers,