This has been a "Trail" recommended product in the past and it has some major advantages over the other units here. Primarily you get a huge flow rate of 1.7 litres per minute, making this ideal for those who want to filter a lot of water quickly.

You also get an inlet pipe that has a prefilter and a float, and you can screw the filter to a "Sigg" or "Nalgene" style water bottle. This makes using this unit fast and very easy to use. It will remove viruses without the addition of iodine due to the 0.1/0.4 micron filter that strains out contaminates, which is a big plus: as there is no iodine, the water tastes great too.