For me this is a great Flash for Hot or Cold liquids. From my tests this actually can keep the temperature for 24 hours. I one of the tests I have made I have tested for 48 hours or so, and the result was pretty good.
The dimension of the flash is great to put on your backpack for daily use, and not just when you go for extremes places and adventures. Good to take our home made tea, coffe or energetic drink to work or to a micro-adventurer.
The space inside for the liquid, in the 500 ml version is good for two standard cups (250ml). If you need more you can go to the 800ml version, for example.
The removable rubber is useful for some grip, but if you don’t like you can remove it.
To pour the water with the lid on, there are two parallel slots/gaps in the lid screw. Unscrew the lid a little bit (0:59 of the video) and use one of the slots/gaps to pour the liquid (the other is for the air I guess). But be careful, not to tilt to much the flash, otherwise the liquid could pass through there as well.
Hope it helps!