Filled this thing to the brim for a three-day trip and the flexible body took up almost no room once it was empty. The threaded cap screwed onto my filter without any adapter fuss, which saved me from hauling a separate bottle.
Fits my gravity filter right out of the box, which was the main reason I grabbed it. The flexible material means it packs down to nothing once it's empty, so it barely took up space in my pack.