I am a competitive mountain bike racer and using these flasks is the fastest way to take on nutrition in the form of gels and keep moving forward. When I don't need to take a full 5 servings with me (meaning a completely full flask of gel) I always add water to thin out the mix. This not only makes the fueling time even quicker but also ensures you get all the gel out a lot easier. I have a buddy that adds a little brewed coffee to his flasks to add some caffeine.
I can't ride and open gels so I have to stop to do that. Then I have to catch up as my buddies are hard core and will not wait on me.
So the flask works. I don't need to stop.
And I have no litter to deal with.
That's about it. A solution to my problem.