Bests & Worsts Reviews from Amazon

There is a A LOT of misinformation in the reviews here (read: those reviews giving it 1 star because water stagnates inside the cup). Pro tip: the flange is housed inside the cup during shipping, which will trap water inside the cup if you don't unfold it. Long story, short, those complaints are caused by user error. You just have to unfold the flange from inside the cup to outside the cup (ideally before your first use).