You can't compare Nalgene bottles to Platypus bags.

The main and deciding difference is bulk. I simply can't use a Nalgene bottle because my entire pocket kit is about the volume of a couple of packs of cigarettes. Even a small Nalgene bottle wouldn't fit. But I can roll up and slip in a pair of half-liter Platypus bottles.

My larger belt kit is all told about the same volume as a liter size Nalgene bottle. It rides in a nylon ALICE pouch meant for M-16 magazines. Two one-liter Platypus bottles fit nicely in there rolled up.

Nalgene bottles are a mainstay of the camping and hiking communities. They are tough and reliable. But they are bulky.

Platypus are comparatively less tough and reliable but IMO they are reliable enough for the intended use. Don't even try to compare the genuine Platypus with the cheap generic versions. Many of those are little better than glorified Baggies. Many of those leak right out of the box.

I have used the Platypus bottles with considerable success. Emergency use, kind of the point behind all those BOBs and kits, your talking about space-critical applications where the choices are much more limited. Your choices are roughly: Condoms, formula bags, Zip-Lock freezer bags, Platypus knock-offs or the genuine article.

Of those viable options for a compact kit, where you can't stuff in a Nalgene bottle or USGI canteen, the Platypus bottles are IMO the most rugged, dependable and capable choice. Which is why I chose them. To some extent I'm less concerned with long-term durability when stocking the survival kit. I'm not homesteading the woods when I'm using my survival kits. I'm on my way out by rescue or walking so if they last two weeks in that roll they have served me well. When I get back to civilization I'll buy more so the ones in the kit are always tested but new.

I find them pretty much durable enough for every-day field use but That's just me. Remember I'm in the SE so water is much less a critical and hard to find resource than if I lived in the arid SW where the next water might be ten miles away. This area is drying out, like most other places, but for the time being I can still find water pretty easily.

If durability is much more a point of worry for you than compactness then you can assemble much larger survival kits and stuff in a couple of Nalgene bottles or regular canteens. Different types of water bottles for different uses and different strokes for different folks.