Rating: 5 / 5
This is all I carry anymore in good weather, the Platypus .5 liter with a pop top on it. Caveat -- all I need is a .5 liter because I have a cooking pot for camp and we have streams and lakes all over the place. The pop top is great. Weighs .7 oz.
Even with the small top opening it is easy to refill using a pump action filter by dropping the hose into the bottle which stands up on its base. In the worst case scenarios I use a pot to get water out of a hard to reach stream or lake, then filter water from the pot into the Platypus in a more convenient spot. (I have not gotten into using chemical treatments so far.)
It is the pop top that makes it so great, easy to use and gets rid of the hydration hose that comes with the bigger sizes. It fits easily into the pack side pockets. Also, it fits in my hip pocket for 2 - 4 hour side trips.
So for weight, quality of construction, practicality, and functionality I give it a 5.