Pros: Lightweight, easy to use, no batteries or moving parts.
Cons: A straw? You're only getting clean water as you need it, by sucking it into your mouth. No clean water stored for later use, or that can be used in other ways, such as mixing water with milk/nutrition powders.
This past summer we used a
SteriPen on a camping trip in Kodiak. The device was fast and simple to use. But it takes batteries to operate - a big drawback. It has a pre-filter for water with sediment.
In past years we've used a Sawyer, some tubing, a bucket, and a water bag to filter large amounts of water by gravity. (We got that idea here at PS.Com) Works brilliantly for a family of four, though it isn't something you'd want to carry around.
Susan