Having been in the military for a few decades and worked in the outdoors, the worst thing EVER, is getting out of a warm sleeping bag in the middle of a freezing night to run outside the shelter/tent/hut/snow-hole etc for a pee.
Having tried numerous methods of combatting this particular problem, which mainly consisted of different sized and shaped bottles, it always came down to lugging 'another' bottle around purely for weeing into.
But now, I feel the search for the 'Holy Grail' of piss bottles is over!
Having the same screw safe and sized top as a regular Nalgene, there's no danger of spillage, allowing use even inside the bag (it was a particularly cold night) and then emptying it the next morning; after the usual shout of "anyone for Lucozade?" it simply rolls up nicely, taking a fraction of the space in your bergen/rucksack.
Probably not what the nice people and all those investment dollars at Nalgene had in mind, but I for one, thank you!