Careful with a sweetwater/MSR Guardian. The folks at Campmor convinced me that a Hiker Pro was the better answer (despite the Guardian's ease of use) b/c the pivot point where the handle attaches to the body can break easily. Not, in a word, "scoutproof", which was one of my criteria.

Hiker Pro fairly easy to use; I do not have a need to kill viruses, though you could accomplish that (same way as the sweetwater) by treating with chemicals after you filter. Chemicals (bleach/iodine) have a long wait time to crack the shell on giardia/other cysts - recommended wait time for bleach used to be 15 minutes, but now is 4 hours else I'd be using chemicals. But don't trust my old research, keep digging for yourself.


PS- Thinking about the chemistry, I'd be careful about trusting a filter to get rid of UNDESIRED chemicals in solution, but I bet you've had as much Chem as I did so you should be able to think about this for yourself.