Bottle leaks no matter what
I love the principle, but the bottle leaks. Doesn't matter if the filter is in or out, or the straw installed or not. The flip-up lid pinches a flexible tube closed which is ok, but the rubber release valve (which lets in air as you suck/squeeze water out) lets water leak out. This is horrible when I want to put it in my camping bag with valuable electronics which don't care for water.
Also, if the bottle is squeezed while in the pack, when you flip the lid open water will squirt out because of the built up pressure. Really horrible design.