The folks at LifeStraw apparently realized the dilemma that occurs when you are hiking and are not going to be able to access a water source consistently. Thus they introduced this bottle series so that you can fill up your bottle with a liter of water whenever you can get to a water source and take it on the go. It has the same straw as the original built in so that you'll get the same filtration effects.

For those who are curious, no you cannot use these straws to drink salt water. The company expressly states as much on their site indicating that the straw does not remove dissolved salts.